<faqs title="Frequently Asked Questions" xmlns="http://maven.apache.org/FML/1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/FML/1.0 http://maven.apache.org/xsd/fml-1.0.xsd">
    <part id="faqinfo">
        <title>About this frequently asked questions list</title>
        <faq id="faqinfo_1">
            <question>Who is responsible for this FAQ?</question>
            <answer>
                <p>The current version of this FAQ is maintained
      by <a href="mailto:mike@clarkware.com">Mike Clark</a>.</p>
                <p>Most of the wisdom contained in this FAQ comes from the
      collective insights and hard-won experiences of the many good
      folks who participate on the JUnit mailing list and the JUnit
      community at large.</p>
                <p>If you see your genius represented anywhere in this FAQ without
      due credit to you, please send me an email and I'll make things
      right.</p>
            </answer>
        </faq>
        <faq id="faqinfo_2">
            <question>How can I contribute to this FAQ?</question>
            <answer>
                <p>Your contributions to this FAQ are greatly appreciated!  The
      JUnit community thanks you in advance.</p>
                <p>To contribute to this FAQ, simply write a JUnit-related question
      and answer, then send the unformatted text
      to 
                    
                    <a href="mailto:mike@clarkware.com">
                        Mike Clark</a>.
      Corrections to this FAQ are always appreciated, as well.</p>
                <p>No reasonable contribution will be denied.  Your name will
      always appear along with any contribution you make.</p>
            </answer>
        </faq>
        <faq id="faqinfo_3">
            <question>Where do I get the latest version of this
      FAQ?</question>
            <answer>
                <p>The master copy of this FAQ is available
      at 
                    
                    <a href="http://junit.sourceforge.net/doc/faq/faq.htm">
                        http://junit.sourceforge.net/doc/faq/faq.htm</a>.</p>
                <p>The JUnit distribution also includes this FAQ in
      the 
                    
                    <code>
                        doc</code>directory.</p>
            </answer>
        </faq>
    </part>
    <part id="overview">
        <title>Overview</title>
  <faq id="overview_1"><question>What is JUnit?</question>    
    <answer><p>
      JUnit is a simple, open source framework to write and run
      repeatable tests. It is an instance of the xUnit architecture
      for unit testing frameworks.  JUnit features include:
    </p>
    <ul>
      <li>Assertions for testing expected results</li>
      <li>Test fixtures for sharing common test data</li>
      <li>Test runners for running tests</li>
    </ul>
    <p>
      JUnit was originally written by Erich Gamma and Kent Beck.
    </p>
</answer>
  </faq>
  <faq id="overview_2"><question>Where is the JUnit home page?</question>
  <answer>
    <p>
      The official JUnit home page is <a
      href="http://junit.org">http://junit.org</a>.
    </p>
</answer>
</faq>
<faq id="overview_3"><question>Where are the JUnit mailing lists and
      forums?</question>
    <answer>
    <p>
      There are 3 mailing lists dedicated to everything JUnit:
    </p>
    <ul>
      <li>
    <a href="http://groups.yahoo.com/group/junit/">JUnit user
    list</a>.  (Search it for answers to frequently asked
    questions not included here.)
      </li>
      <li>
    <a
    href="http://lists.sourceforge.net/lists/listinfo/junit-announce">JUnit
    announcements</a>
      </li>
      <li>
    <a
    href="http://lists.sourceforge.net/lists/listinfo/junit-devel">JUnit
    developer list</a>
      </li>
    </ul>
</answer>
</faq>
<faq id="overview_4"><question>Where is the JUnit
      documentation?</question>
<answer>
    <p>
      The following documents are included in the JUnit distribution
      in the <code>doc</code> directory:
    </p>
    <ul>
      <li>
    <a
    href="http://junit.sourceforge.net/doc/testinfected/testing.htm">JUnit
    Test Infected: Programmers Love Writing Tests</a>
      </li> 
      <li>
    <a
    href="http://junit.sourceforge.net/doc/cookbook/cookbook.htm">JUnit
      Cookbook</a>
      </li>
      <li>
    <a
    href="http://junit.sourceforge.net/doc/cookstour/cookstour.htm">JUnit
    - A Cook's Tour</a>
      </li>
      <li>
    <a href="http://junit.sourceforge.net/doc/faq/faq.htm">JUnit
    FAQ</a>
      </li>
    </ul>
</answer>
</faq>
<faq id="overview_5"><question>Where can I find articles on
      JUnit?</question><answer>
    <p>
      The JUnit home page maintains a list
      of <a href="http://www.junit.org/news/article/index.htm">JUnit
      articles</a>.
    </p>
</answer>
</faq>
  <faq id="overview_6"><question>What's the latest news on JUnit?</question>
  <answer>
    <p>
      The JUnit home page publishes
      the <a href="http://www.junit.org/news/index.htm">latest JUnit
      news</a>.
    </p>
</answer>
</faq>
      <faq id="overview_7"><question>How is JUnit licensed?</question>
      <answer>
    <p>
      JUnit is <a href="http://www.opensource.org/">Open Source
      Software</a>, released
      under the <a
      href="http://opensource.org/licenses/eclipse-1.0.html">
      Eclipse Public License Version 1.0</a> and hosted
      on <a
      href="http://sourceforge.net/projects/junit/">SourceForge</a>.
    </p>
</answer>
</faq>
  <faq id="overview_8"><question>What awards has JUnit won?</question>
<answer>
    <ul>
      <li>
    <p> <a
    href="http://www.javaworld.com/javaworld/jw-03-2002/jw-0326-awards.html">2002
    JavaWorld Editors' Choice Awards (ECA)</a>
    </p>
    <p>
      Best Java Performance Monitoring/Testing Tool
    </p>
      </li>
      <li>
    <p>
      <a
      href="http://www.javaworld.com/javaworld/jw-06-2001/j1-01-awards.html">2001
      JavaWorld Editors' Choice Awards (ECA)</a>
    </p>
    <p>
      Best Java Performance Monitoring/Testing Tool
    </p>
      </li>
    </ul>
</answer>
</faq>
    </part>
    <part id="started">
        <title>Getting Started</title>
        <faq id="started_1">
            <question>Where do I download JUnit?</question>
            <answer><p>
      The latest version of JUnit is available
      on <a
      href="http://sourceforge.net/project/showfiles.php?group_id=15278">SourceForge</a>.
    </p></answer>
        </faq>
        <faq id="started_2">
            <question>How do I install JUnit?</question>
            <answer><ol>
      <li>
    <p>
      First, <a
            href="http://sourceforge.net/project/showfiles.php?group_id=15278">download</a>
      the
      latest version of JUnit, referred to below
      as <code>junit.zip</code>. 
    </p>
      </li>
      <li>
    <p>
      Then install JUnit on your platform of choice:
    </p>
    <p>
      <u>Windows</u>
    </p>
    <p>
      To install JUnit on Windows, follow these steps:
    </p>
    <ol>
      <li>
        <p>
          Unzip the <code>junit.zip</code> distribution file to
          a directory referred to as <code>%JUNIT_HOME%</code>.
        </p>
      </li>
      <li>Add JUnit to the classpath:
        <p>
          <code>set CLASSPATH=%CLASSPATH%;%JUNIT_HOME%\junit.jar</code>
        </p>
      </li>
    </ol>
    <p>
      <u>Unix (bash)</u>
    </p>
    <p>
      To install JUnit on Unix, follow these steps:
    </p>
    <ol>
      <li>
        <p>
          Unzip the <code>junit.zip</code> distribution file to
          a directory referred to as <code>$JUNIT_HOME</code>.
        </p>    
      </li>
      <li>
        <p>
          Add JUnit to the classpath:
        </p>
        <p>
          <code>export CLASSPATH=$CLASSPATH:$JUNIT_HOME/junit.jar</code>
        </p>
      </li>
    </ol>
      </li>
      <li>
    <p>
      <i>(Optional)</i> Unzip
      the <code>$JUNIT_HOME/src.jar</code> file.
    </p>
      </li>
      <li>
    <p>
      Test the installation by running the sample tests
      distributed with JUnit.  Note that the sample tests are
      located in the installation directory directly, not
      the <code>junit.jar</code> file.  Therefore, make sure that
      the JUnit installation directory is on your CLASSPATH.  Then
      simply type:
    </p>
    <pre>java org.junit.runner.JUnitCore org.junit.tests.AllTests</pre>
    <p>
      All the tests should pass with an "OK" message.
    </p>
    <p>
      <i> 
        If the tests don't pass, verify
        that <code>junit.jar</code> is in the CLASSPATH.
      </i>
    </p>
      </li>
      <li>
    <p>
      Finally, <a href="#overview_4">read</a> the documentation.
    </p>
      </li>
    </ol></answer>
        </faq>
        <faq id="started_3">
            <question>How do I uninstall JUnit?</question>
            <answer><ol>
      <li>
    <p> 
      Delete the directory structure where you unzipped the JUnit
      distribution.
    </p>
      </li>
      <li>
    <p>
      Remove <code>junit.jar</code> from the CLASSPATH.
    </p>
      </li>
    </ol>
    <p>
      JUnit does not modify the registry so simply removing all the
      files will fully uninstall it.
    </p></answer>
        </faq>
        <faq id="started_4">
            <question>How do I ask questions?</question>
            <answer><p>
      Questions that are not answered in
      the <a
      href="http://junit.sourceforge.net/doc/faq/faq.htm">FAQ</a> or
      in the <a href="#overview_4">documentation</a> should be posted
      to
      the <a
      href="http://www.jguru.com/forums/home.jsp?topic=JUnit">jGuru
    discussion forum</a> or the <a
    href="http://groups.yahoo.com/group/junit/">JUnit user mailing
    list</a>.
    </p>
    <p>
      Please stick to technical issues on the discussion forum and
      mailing lists. Keep in mind that these are public, so
      do <b>not</b> include any confidental information in your
      questions!
    </p>
    <p>
      You should also
      read <a
      href="http://www.catb.org/~esr/faqs/smart-questions.html">"How
      to ask questions the smart way"</a> by Eric Raymond before
      participating in the discussion forum and mailing lists.
    </p>
    <p>
      <i> 
    NOTE: <br/> Please do NOT submit bugs, patches, or feature
    requests to the discussion forum or mailing lists.  <br/>
    Refer instead to <a href="#started_5">"How do I submit bugs,
    patches, or feature requests?"</a>.
      </i>
    </p></answer>
        </faq>
        <faq id="started_5">
            <question>How do I submit bugs, patches, or
       feature requests?</question>
            <answer>    <p>
      JUnit celebrates programmers testing their own software. In this
      spirit, bugs, patches, and feature requests that include JUnit
      tests have a better chance of being addressed than those
      without.
    </p>
    <p>
      JUnit is hosted
      on <a
      href="http://github/junit-team/junit">GitHub</a>.
      Please use the tools provided by GitHub for your
      submissions.
    </p>
</answer>
        </faq>
    </part>
    <part id="tests">
        <title>Writing Tests</title>
      <faq id="#tests_1"><question>How do I write and run a simple test?</question><answer>    <ol>
      <li>
    <p>
      Create a class:
    </p>
<pre class="prettyprint linenums">package junitfaq;
      
import org.junit.*;
import static org.junit.Assert.*;

import java.util.*;

public class SimpleTest {</pre>      
      </li>
      <li>
    <p>
      Write a test method (annotated with <code>@Test</code>) that
      asserts expected results on the object under test:
    </p>
    <pre class="prettyprint linenums">    @Test
    public void testEmptyCollection() {
        Collection collection = new ArrayList();
        assertTrue(collection.isEmpty());
    }</pre>
      </li>
      <li>
    <p>
      If you are running your JUnit 4 tests with a JUnit 3.x runner,
      write a <code>suite()</code> method that uses the 
      <code>JUnit4TestAdapter</code> class to create a suite
      containing all of your test methods:
    </p>
    <pre class="prettyprint linenums">    public static junit.framework.Test suite() {
        return new junit.framework.JUnit4TestAdapter(SimpleTest.class);
    }</pre>
      </li>
      <li>
    <p>
      Although writing a <code>main()</code> method to run the
      test is much less important with the advent of IDE runners,
      it's still possible:
    </p>
    <pre class="prettyprint linenums">    public static void main(String args[]) {
      org.junit.runner.JUnitCore.main("junitfaq.SimpleTest");
    }
}</pre>
      </li>
      <li>
    <p>
      Run the test:
    </p>
    <ul>
      <li>
        <p>
          To run the test from the console, type:
        </p>
        <pre>java org.junit.runner.JUnitCore junitfaq.SimpleTest</pre>
      </li>
      <li>
        <p>
          To run the test with the test runner used
          in <code>main()</code>, type:
        </p>
        <pre>java junitfaq.SimpleTest</pre> 
      </li>
    </ul>
    <p>
      The passing test results in the following textual output:
    </p>
    <pre>.
Time: 0

OK (1 tests)</pre>
      </li>
    </ol>
</answer></faq>
      <faq id="#tests_2"><question>How do I use a test fixture?</question><answer><p>
      <i>(Submitted by: Jeff Nielsen)</i>
    </p>
    <p>
      A test fixture is useful if you have two or more tests for a
      common set of objects.  Using a test fixture avoids duplicating
      the code necessary to initialize (and cleanup) the common
      objects.
    </p>
    <p>
      Tests can use the objects (variables) in a test fixture, with
      each test invoking different methods on objects in the fixture
      and asserting different expected results.  Each test runs in its
      own test fixture to isolate tests from the changes made by other
      tests.  That is, <em>tests don't share the state of objects in
      the test fixture</em>.  Because the tests are isolated, they can
      be run in any order.
    </p>
    <p>
      To create a test fixture, declare instance variables for the
      common objects.  Initialize these objects in a <code>public
      void</code> method annotated with <code>@Before</code>.  The
      JUnit framework automatically invokes any <code>@Before</code>
      methods before each test is run.
    </p>
    <p>
      The following example shows a test fixture with a common
      <code>Collection</code> object.
    </p>
    <pre class="prettyprint linenums">package junitfaq;

import org.junit.*;
import static org.junit.Assert.*;
import java.util.*;

public class SimpleTest {

    private Collection&lt;Object&gt; collection;

    @Before
    public void setUp() {
        collection = new ArrayList&lt;Object&gt;();
    }

    @Test
    public void testEmptyCollection() {
        assertTrue(collection.isEmpty());
    }


    @Test
    public void testOneItemCollection() {
        collection.add("itemA");
        assertEquals(1, collection.size());
    }
}</pre>

    <p>
      Given this test, the methods might execute in the following
      order:
    </p>
      <pre class="prettyprint linenums">setUp()
testEmptyCollection()
setUp()
testOneItemCollection()</pre>
    <p>
      The ordering of test-method invocations is not guaranteed, so
      <code>testOneItemCollection()</code> might be executed before
      <code>testEmptyCollection()</code>.  But it doesn't matter,
      because each method gets its own instance of the
      <code>collection</code>.
    </p>

    <p>
      Although JUnit provides a new instance of the fixture objects
      for each test method, if you allocate any <em>external</em>
      resources in a <code>@Before</code> method, you should release
      them after the test runs by annotating a method with
      <code>@After</code>.  The JUnit framework automatically invokes
      any <code>@After</code> methods after each test is run.  For
      example:
    </p>

    <pre class="prettyprint linenums">package junitfaq;

import org.junit.*;
import static org.junit.Assert.*;
import java.io.*;

public class OutputTest {

    private File output;

    @Before
    public void createOutputFile() {
        output = new File(...);
    }

    @After
    public void deleteOutputFile() {
        output.delete();
    }

    @Test
    public void testSomethingWithFile() {
        ...
    }
}</pre>
    <p>
      With this test, the methods will execute in the following order:
    </p>
    <pre class="prettyprint linenums">
createOutputFile()
testSomethingWithFile()
deleteOutputFile()</pre></answer></faq>
      <faq id="#tests_4"><question>How do I test a method that doesn't
      return anything?</question><answer><p>
      <i>(Submitted by: Dave Astels)</i>
    </p>
    <p>
      Often if a method doesn't return a value, it will have some side
      effect. Actually, if it doesn't return a value AND doesn't have
      a side effect, it isn't doing anything.
    </p>
    <p>
      There may be a way to verify that the side effect actually
      occurred as expected. For example, consider
      the <code>add()</code> method in the Collection classes. There
      are ways of verifying that the side effect happened (i.e. the
      object was added). You can check the size and assert that it is
      what is expected:
    </p>
    <pre class="prettyprint linenums">
    @Test
    public void testCollectionAdd() {
        Collection collection = new ArrayList();
        assertEquals(0, collection.size());
        collection.add("itemA");
        assertEquals(1, collection.size());
        collection.add("itemB");
        assertEquals(2, collection.size());
    }</pre>
    <p>
      Another approach is to make use of <a
      href="http://www.mockobjects.com">MockObjects</a>.
    </p>
    <p>
      A related issue is to design for testing. For example, if you
      have a method that is meant to output to a file, don't pass in a
      filename, or even a <code>FileWriter</code>. Instead, pass in
      a <code>Writer</code>. That way you can pass in
      a <code>StringWriter</code> to capture the output for testing
      purposes. Then you can add a method
      (e.g. <code>writeToFileNamed(String filename)</code>) to
      encapsulate the <code>FileWriter</code> creation.
    </p></answer></faq>
      <faq id="#tests_5"><question>Under what conditions should I test get()
      and set() methods?</question><answer><p>
      Unit tests are intended to alleviate fear that something might
      break.  If you think a <code>get()</code> or <code>set()</code>
      method could reasonably break, or has in fact contributed to a
      defect, then by all means write a test.
    </p>
    <p>
      In short, test until you're confident.  What you choose to test
      is subjective, based on your experiences and confidence level.
      Remember to be practical and maximize your testing investment.
    </p>
    <p>  
      Refer also to <a href="#best_3">"How simple is 'too simple to
      break'?"</a>.
    </p></answer></faq>
      <faq id="#tests_6"><question>Under what conditions should I not test
      get() and set() methods?</question><answer><p>
      <i>(Submitted by: J. B. Rainsberger)</i>
    </p>
    <p>
      Most of the time, get/set methods just can't break, and if they
      can't break, then why test them? While it is usually better to
      test more, there is a definite curve of diminishing returns on
      test effort versus "code coverage".  Remember the maxim: "Test
      until fear turns to boredom."
    </p>
    <p>
      Assume that the <code>getX()</code> method only does "return x;"
      and that the <code>setX()</code> method only does "this.x =
      x;". If you write this test:
    </p>
    <pre class="prettyprint linenums">@Test
public void testGetSetX() {
    setX(23);
    assertEquals(23, getX());
}</pre>
    <p>
      then you are testing the equivalent of the following:
    </p>
    <pre class="prettyprint linenums">
@Test
public void testGetSetX() {
    x = 23;
    assertEquals(23, x);
}</pre>
    <p>
      or, if you prefer,
    </p>
    <pre class="prettyprint linenums">@Test
public void testGetSetX() {
    assertEquals(23, 23);
}</pre>
    <p>
      At this point, you are testing the Java compiler, or possibly
      the interpreter, and not your component or application. There is
      generally no need for you to do Java's testing for them.
    </p>
    <p>
      If you are concerned about whether a property has already been
      set at the point you wish to call <code>getX()</code>, then you
      want to test the constructor, and not the <code>getX()</code>
      method. This kind of test is especially useful if you have
      multiple constructors:
    </p>
    <pre class="prettyprint linenums">@Test
public void testCreate() {
    assertEquals(23, new MyClass(23).getX());
}</pre>
</answer></faq>
      <faq id="#tests_7"><question>How do I write a test that passes when an
      expected exception is thrown?</question><answer><p>
      Add the optional <code>expected</code> attribute to
      the <code>@Test</code> annotation.  The following is an example
      test that passes when the
      expected <code>IndexOutOfBoundsException</code> is raised:
    </p>
    <pre class="prettyprint linenums">@Test(expected=IndexOutOfBoundsException.class)
public void testIndexOutOfBoundsException() {
    ArrayList emptyList = new ArrayList();
    Object o = emptyList.get(0);
}</pre>
    </answer></faq>
      <faq id="#tests_8"><question>How do I write a test that fails when an
      unexpected exception is thrown?</question><answer><p>
      Declare the exception in the <code>throws</code> clause of the
      test method and don't catch the exception within the test
      method.  Uncaught exceptions will cause the test to fail with an
      error.
    </p>
    <p>
      The following is an example test that fails when
      the <code>IndexOutOfBoundsException</code> is raised:
    </p>
    <pre class="prettyprint linenums">@Test
public void testIndexOutOfBoundsExceptionNotRaised() 
    throws IndexOutOfBoundsException {

    ArrayList emptyList = new ArrayList();
    Object o = emptyList.get(0);
}</pre></answer></faq>
      <faq id="#tests_10"><question>How do I test protected methods?</question><answer><p>
      Place your tests in the same package as the classes under test.
    </p>
    <p>
      Refer to <a href="#organize_1">"Where should I put my test
      files?"</a> for examples of how to organize tests for protected
      method access.
    </p></answer></faq>
      <faq id="#tests_11"><question>How do I test private methods?</question><answer><p>
      Testing private methods may be an indication that those methods
      should be moved into another class to promote reusability.
    </p>
    <p>
      But if you must...
    </p>
    <p>
      If you are using JDK 1.3 or higher, you can use reflection to
      subvert the access control mechanism with the aid of
      the <a
      href="http://sourceforge.net/projects/privaccessor/">PrivilegedAccessor</a>.
      For details on how to use it,
      read <a
      href="http://www.onjava.com/pub/a/onjava/2003/11/12/reflection.html">this
      article</a>.
    </p></answer></faq>
      <faq id="#tests_12"><question>Why does JUnit only report the first
      failure in a single test?</question><answer><p>
      <i>(Submitted by: J. B. Rainsberger)</i>
    </p>
    <p>
      Reporting multiple failures in a single test is generally a sign
      that the test does too much, compared to what a unit test ought
      to do. Usually this means either that the test is really a
      functional/acceptance/customer test or, if it is a unit test,
      then it is too big a unit test.
    </p>
    <p>
      JUnit is designed to work best with a number of small tests. It
      executes each test within a separate instance of the test
      class. It reports failure on each test. Shared setup code is
      most natural when sharing between tests. This is a design
      decision that permeates JUnit, and when you decide to report
      multiple failures per test, you begin to fight against
      JUnit. This is not recommended.
    </p>
    <p>
      Long tests are a design smell and indicate the likelihood of a
      design problem. Kent Beck is fond of saying in this case that
      "there is an opportunity to learn something about your design."
      We would like to see a pattern language develop around these
      problems, but it has not yet been written down.
    </p>
    <p>
      Finally, note that a single test with multiple assertions is
      isomorphic to a test case with multiple tests:
    </p>
    <p>
      One test method, three assertions:
    </p>
    <pre class="prettyprint linenums">public class MyTestCase {
    @Test
    public void testSomething() {
        // Set up for the test, manipulating local variables
        assertTrue(condition1);
        assertTrue(condition2);
        assertTrue(condition3);
    }
}</pre>
    <p>
      Three test methods, one assertion each:
    </p>
    <pre class="prettyprint linenums">
public class MyTestCase {
    // Local variables become instance variables

    @Before
    public void setUp() {
        // Set up for the test, manipulating instance variables
    }
    
    @Test
    public void testCondition1() {
        assertTrue(condition1);
    }

    @Test
    public void testCondition2() {
        assertTrue(condition2);
    }

    @Test
    public void testCondition3() {
        assertTrue(condition3);
    }
}</pre>
    <p>
      The resulting tests use JUnit's natural execution and reporting
      mechanism and, failure in one test does not affect the execution
      of the other tests.  You generally want exactly one test to fail
      for any given bug, if you can manage it.
    </p></answer></faq>
      <faq id="#tests_13"><question>In Java 1.4, 'assert' is a
      keyword. Won't this conflict with JUnit's assert()
      method?</question><answer><p>
      JUnit 3.7 deprecated <code>assert()</code> and replaced it
      with <code>assertTrue()</code>, which works exactly the same
      way.
    </p>
    <p>
      JUnit 4 is compatible with the <code>assert</code> keyword.  If
      you run with the <code>-ea</code> JVM switch, assertions that
      fail will be reported by JUnit.
    </p></answer></faq>
      <faq id="#tests_14"><question>How do I test things that must be run in
      a J2EE container (e.g. servlets, EJBs)?</question><answer><p>
      Refactoring J2EE components to delegate functionality to other
      objects that don't have to be run in a J2EE container will
      improve the design and testability of the software.
    </p>
    <p>
      <a href="http://jakarta.apache.org/cactus/index.html">Cactus</a>
      is an open source JUnit extension that can be used to test J2EE
      components in their natural environment.
    </p></answer></faq>
      <faq id="#tests_15"><question>Do I need to write a test class for
      every class I need to test?</question><answer><p>
      <i>(Submitted by: J. B. Rainsberger)</i>
    </p>
    <p>
      No. It is a convention to start with one test
      class per class under test, but it is not necessary.
    </p>
    <p>
      Test classes only provide a way to organize tests, nothing more.
      Generally you will start with one test class per class under
      test, but then you may find that a small group of tests belong
      together with their own common test fixture.[1] In this case,
      you may move those tests to a new test class.  This is a simple
      object-oriented refactoring: separating responsibilities of an
      object that does too much.
    </p>
    <p>
      Another point to consider is that the <code>TestSuite</code> is
      the smallest execution unit in JUnit: you cannot execute
      anything smaller than a TestSuite at one time without changing
      source code. In this case, you probably do not want to put tests
      in the same test class unless they somehow "belong together".
      If you have two groups of tests that you think you'd like to
      execute separately from one another, it is wise to place them in
      separate test classes.
    </p>
    <p>
      <i>
    [1] A test fixture is a common set of test data and
    collaborating objects shared by many tests. Generally they are
    implemented as instance variables in the test class.
      </i>
    </p></answer></faq>
      <faq id="#tests_16"><question>Is there a basic template I can use to
      create a test?</question><answer><p>
      <i>(Submitted by: Eric Armstrong)</i>
    </p>
    <p>
      The following templates are a good starting point.  Copy/paste
      and edit these templates to suit your coding style.
    </p>
    <p>
      SampleTest is a basic test template:
    </p>
    <pre class="prettyprint linenums">import org.junit.*;
import static org.junit.Assert.*;

public class SampleTest {

    private java.util.List emptyList;

    /**
     * Sets up the test fixture. 
     * (Called before every test case method.)
     */
    @Before
    public void setUp() {
        emptyList = new java.util.ArrayList();
    }

    /**
     * Tears down the test fixture. 
     * (Called after every test case method.)
     */
    @After
    public void tearDown() {
        emptyList = null;
    }
    
    @Test
    public void testSomeBehavior() {
        assertEquals("Empty list should have 0 elements", 0, emptyList.size());
    }

    @Test(expected=IndexOutOfBoundsException.class)
    public void testForException() {
        Object o = emptyList.get(0);
    }
}</pre></answer></faq>
      <faq id="#tests_17"><question>How do I write a test for an abstract
      class?</question><answer><p>
      Refer to <a
      href="http://c2.com/cgi/wiki?AbstractTestCases">http://c2.com/cgi/wiki?AbstractTestCases</a>.
    </p></answer></faq>
      <faq id="#tests_18"><question>When are tests garbage collected?</question><answer><p>
      <i>(Submitted by: Timothy Wall and Kent Beck)</i>
    </p>
    <p>
      By design, the tree of Test instances is built in one pass, then
      the tests are executed in a second pass.  The test runner holds
      strong references to all Test instances for the duration of the
      test execution.  This means that for a very long test run with
      many Test instances, none of the tests may be garbage collected
      until the end of the entire test run.
    </p>
    <p>
      Therefore, if you allocate external or limited resources in a
      test, you are responsible for freeing those resources.
      Explicitly setting an object to <code>null</code> in
      the <code>tearDown()</code> method, for example, allows it to be
      garbage collected before the end of the entire test run.
    </p></answer></faq>
    </part>
    <part id="organize">
        <title>Organizing Tests</title>
        <faq id="organize_1">
            <question>Where should I put my test files?</question>
            <answer><p>
      You can place your tests in the same package and directory as
      the classes under test.
    </p>
    <p>
      For example:
    </p>
    <pre>src
   com
      xyz
         SomeClass.java
         SomeClassTest.java</pre>
    <p> 
      While adequate for small projects, many developers feel that
      this approach clutters the source directory, and makes it hard
      to package up client deliverables without also including
      unwanted test code, or writing unnecessarily complex packaging
      tasks.
    </p>
    <p>
      An arguably better way is to place the tests in a separate
      parallel directory structure with package alignment.
    </p>
    <p>
      For example:
    </p>
    <pre>src
   com
      xyz
         SomeClass.java
test
   com
      xyz
         SomeClassTest.java</pre>
    <p>
      These approaches allow the tests to access to all the public and
      package visible methods of the classes under test.
    </p>
    <p>
      Some developers have argued in favor of putting the tests in a
      sub-package of the classes under test (e.g. com.xyz.test). The
      author of this FAQ sees no clear advantage to adopting this
      approach and believes that said developers also put their curly
      braces on the wrong line.  :-)
    </p></answer>
        </faq>
        <faq id="organize_3">
            <question>How can I run setUp() and tearDown()
      code once for all of my tests?</question>
            <answer><p>
      The desire to do this is usually a symptom of excessive coupling
      in your design.  If two or more tests must share the same test
      fixture state, then the tests may be trying to tell you that the
      classes under test have some undesirable dependencies.
    </p>
    <p>
      Refactoring the design to further decouple the classes under
      test and eliminate code duplication is usually a better
      investment than setting up a shared test fixture.
    </p>
    <p>
      But if you must...
    </p>
    <p>
      You can add a <code>@BeforeClass</code> annotation to a method
      to be run before all the tests in a class, and
      a <code>@AfterClass</code> annotation to a method to be run
      after all the tests in a class.  Here's an example:
    </p>
    <pre class="prettyprint linenums">package junitfaq;

import org.junit.*;
import static org.junit.Assert.*;
import java.util.*;

public class SimpleTest {

    private Collection collection;
    
    @BeforeClass
    public static void oneTimeSetUp() {
        // one-time initialization code        
    }

    @AfterClass
    public static void oneTimeTearDown() {
        // one-time cleanup code
    }

    @Before
    public void setUp() {
        collection = new ArrayList();
    }
    
    @After
    public void tearDown() {
        collection.clear();
    }

    @Test
    public void testEmptyCollection() {
        assertTrue(collection.isEmpty());
    }
    
    @Test
    public void testOneItemCollection() {
        collection.add("itemA");
        assertEquals(1, collection.size());
    }
}</pre>
    <p>
      Given this test, the methods will execute in the following
      order:
    </p>
    <pre class="prettyprint linenums">oneTimeSetUp()
setUp()
testEmptyCollection()
tearDown()
setUp()
testOneItemCollection()
tearDown()
oneTimeTearDown()</pre>
</answer>
        </faq>
    </part>
    <part id="running-tests">
        <title>Running Tests</title>
        <faq id="running_1">
            <question>What CLASSPATH settings are needed to
      run JUnit?</question>
            <answer><p>
      <i>(Submitted by: Eric Armstrong)</i>
    </p>
    <p>
      To run your JUnit tests, you'll need the following elemements in
      your CLASSPATH:
    </p>
    <ul>
      <li>JUnit class files</li>
      <li>Your class files, including your JUnit test classes</li>
      <li>Libraries your class files depend on</li>
    </ul>
    <p>
      If attempting to run your tests results in
      a <code>NoClassDefFoundError</code>, then something is missing
      from your CLASSPATH.
    </p>
    <p>
      <u>Windows Example:</u>
    </p>
    <pre>set CLASSPATH=%JUNIT_HOME%\junit.jar;c:\myproject\classes;c:\myproject\lib\something.jar</pre>
    <p>
      <u>Unix (bash) Example:</u>
    </p>
    <pre>export CLASSPATH=$JUNIT_HOME/junit.jar:/myproject/classes:/myproject/lib/something.jar</pre>
</answer>
        </faq>
        <faq id="running_2">
            <question>Why do I get
        a <code>NoClassDefFoundError</code> when trying to test JUnit
        or run the samples?</question>
            <answer><p>
      <i>(Submitted by: J.B. Rainsberger and Jason Rogers)</i>
    </p>
    <p>
      Most likely your CLASSPATH doesn't include the JUnit
      installation directory.
    </p>
    <p>
      Refer to <a href="#running_1">"What CLASSPATH settings are
      needed to run JUnit?"</a> for more guidance.
    </p>
    <p>
      Also consider running <a
                               href="http://www.clarkware.com/software/WhichJUnit.zip">WhichJunit</a>
      to print the absolute location of the JUnit class files required
      to run and test JUnit and its samples.
    </p>
    <p>
      If the CLASSPATH seems mysterious, read <a
      href="http://java.sun.com/j2se/1.4/docs/tooldocs/findingclasses.html">this</a>!
    </p></answer>
        </faq>
        <faq id="running_4">
            <question>How do I run JUnit from my command window?</question>
            <answer><p>
      <i>(Submitted by: Eric Armstrong)</i>
    </p>
    <ol>
      <li>
        <p>
          <a href="#running_1">Set your CLASSPATH</a>
        </p>
      </li>
      <li>
        <p>
          Invoke the runner:
        </p>
        <p>
          <code>
            java org.junit.runner.JUnitCore &lt;test class name&gt; 
          </code>
        </p>
      </li>
    </ol></answer>
        </faq>
        <faq id="running_5">
            <question>How do I run JUnit using Ant?</question>
            <answer><p>
      <i>(Submitted by: Eric Armstrong)</i>
    </p>
    <ol>
      <li>
        <p>
          Define any necessary Ant properties:
        </p>
          <pre class="prettyprint linenums">&lt;property name="src" value="./src" /&gt;
&lt;property name="lib" value="./lib" /&gt;
&lt;property name="classes" value="./classes" /&gt;
&lt;property name="test.class.name" value="com.xyz.MyTestSuite" /&gt;</pre>
      </li>
      <li>
        <p>
          Set up the CLASSPATH to be used by JUnit:
        </p>
          <pre class="prettyprint linenums">&lt;path id="test.classpath"&gt;
  &lt;pathelement location="${classes}" /&gt;
  &lt;pathelement location="/path/to/junit.jar" /&gt;
  &lt;fileset dir="${lib}">
    &lt;include name="**/*.jar"/&gt;
  &lt;/fileset&gt;
&lt;/path&gt;</pre>
      </li>
      <li>
        <p>
          Define the Ant task for running JUnit:
        </p>
          <pre class="prettyprint linenums">&lt;target name="test"&gt;
  &lt;junit fork="yes" haltonfailure="yes"&gt;
    &lt;test name="${test.class.name}" /&gt;
    &lt;formatter type="plain" usefile="false" /&gt;
    &lt;classpath refid="test.classpath" /&gt;
  &lt;/junit&gt;
&lt;/target&gt;</pre>
      </li>
      <li>
        <p>
          Run the test:
        </p>
        <pre>ant test</pre>
      </li>
    </ol>
    <p>
      Refer to the <a
      href="http://jakarta.apache.org/ant/manual/OptionalTasks/junit.html">JUnit
      Ant Task</a> for more information.
    </p></answer>
        </faq>
        <faq id="running_6">
            <question>How do I use Ant to create HTML test
      reports?</question>
            <answer><p>
      <i>(Submitted by: Eric Armstrong and Steffen Gemkow)</i>
    </p>
    <ol>
      <li>
        <p>
          Ensure that Ant's <code>optional.jar</code> file is either
          in your CLASSPATH or exists in
          your <code>$ANT_HOME/lib</code> directory.
        </p>
      </li>
      <li>
        <p>
          Add an ANT property for the directory containing the HTML reports:
        </p>
        <pre class="prettyprint linenums">&lt;property name="test.reports" value="./reports" /&gt;</pre>
      </li>
      <li>
        <p>
          Define the Ant task for running JUnit and generating reports:
        </p>
          <pre class="prettyprint linenums">&lt;target name="test-html"&gt;
  &lt;junit fork="yes" printsummary="no" haltonfailure="no"&gt;
    &lt;batchtest fork="yes" todir="${test.reports}" &gt;
      &lt;fileset dir="${classes}"&gt;
        &lt;include name="**/*Test.class" /&gt;
      &lt;/fileset&gt;
    &lt;/batchtest&gt;
    &lt;formatter type="xml" /&gt;
    &lt;classpath refid="test.classpath" /&gt;
  &lt;/junit&gt;

  &lt;junitreport todir="${test.reports}"&gt;
    &lt;fileset dir="${test.reports}"&gt;
      &lt;include name="TEST-*.xml" /&gt;
    &lt;/fileset&gt;
    &lt;report todir="${test.reports}" /&gt;
  &lt;/junitreport&gt;
&lt;/target&gt;</pre>
      </li>
      <li>
        <p>
          Run the test:
        </p>
        <div>
          <code>
            ant test-html
          </code>
        </div>
      </li>
    </ol>
    <p>
      Refer to the 
      <a href="http://jakarta.apache.org/ant/manual/OptionalTasks/junit.html">JUnit Ant Task</a>
      for more information.
    </p></answer>
        </faq>
        <faq id="running_7">
            <question>How do I pass command-line arguments
      to a test execution?</question>
            <answer><p>
      Use the <tt>-D</tt> JVM command-line options, as in:
    </p>
    <pre class="prettyprint">-DparameterName=parameterValue</pre>
    <p>
      If the number of parameters on the command line gets unweildy,
      pass in the location of a property file that defines a set of
      parameters. Alternatively, the <a
      href="http://junit-addons.sf.net">JUnit-addons package</a>
      contains the <tt>XMLPropertyManager</tt>
      and <tt>PropertyManager</tt> classes that allow you to define a
      property file (or XML file) containing test parameters.
    </p></answer>
        </faq>
        <faq id="running_9">
            <question>Why do I get
      a <code>LinkageError</code> when using
        XML interfaces in my test?</question>
            <answer><p>
      <i>(Submitted by: Scott Stirling)</i>
    </p>
    <p>
      The workaround as of JUnit 3.7 is to
      add <code>org.w3c.dom.*</code> and <code>org.xml.sax.*</code> to
      your <code>excluded.properties</code>.
    </p>
    <p>
      It's just a matter of time before this fix becomes incorporated
      into the released version of
      JUnit's <code>excluded.properties</code>, since JAXP is a
      standard part of JDK 1.4. It will be just like
      excluding <code>org.omg.*</code>. By the way, if you download
      the JUnit source from its Sourceforge CVS, you will find that
      these patterns have already been added to the default
      excluded.properties and so has a pattern for JINI. In fact, here
      is the current version in CVS, which demonstrates how to add
      exclusions to the list too:
    </p>
    <pre class="prettyprint linenums">#
# The list of excluded package paths for the TestCaseClassLoader
#
excluded.0=sun.*
excluded.1=com.sun.*
excluded.2=org.omg.*
excluded.3=javax.*
excluded.4=sunw.*
excluded.5=java.*
excluded.6=org.w3c.dom.*
excluded.7=org.xml.sax.*
excluded.8=net.jini.*</pre>
    <p>
      This is the most common case where the
      default <code>excluded.properties</code> list needs
      modification. The cause of the <code>LinkageError</code> is
      related to using JAXP in your test cases. By JAXP I mean the
      whole set of <code>javax.xml.*</code> classes and the
      supporting <code>org.w3c.dom.*</code>
      and <code>org.xml.sax.*</code> classes.
    </p>
    <p>
      As stated above, the JUnit GUI TestRunners' classloader relies
      on the <code>excluded.properties</code> for classes it should
      delegate to the system classloader. JAXP is an unusual case
      because it is a standard Java extension library dependent on
      classes whose package names (<code>org.w3c.dom.*</code>
      and <code>org.xml.sax.*</code>) do not begin with a standard
      Java or Sun prefix. This is similar to the relationship
      between <code>javax.rmi.*</code> and the <code>org.omg.*</code>
      classes, which have been excluded by default in
      JUnit'ss <code>excluded.properties</code> for a while.
    </p>
    <p>
      What can happen, and frequently does when using the JUnit Swing
      or AWT UI with test cases that reference, use or depend on JAXP
      classes, such as Log4J, Apache SOAP, Axis, Cocoon, etc., is that
      the JUnit class loader (properly)
      delegates <code>javax.xml.*</code> classes it &quot;sees&quot;
      to the system loader. But then the system loader, in the process
      of initializing and loading that JAXP class, links and loads up
      a bunch of <code>org.w3c.dom</code>/<code>org.xml.sax</code>
      classes. When it does so, the JUnit custom classloader is not
      involved at all because the system classloader never delegates
      &quot;down&quot; or checks with custom classloaders to see if a
      class is already loaded. At any point after this, if the JUnit
      loader is asked to load
      an <code>org.w3c.dom</code>/<code>org.xml.sax</code> class that
      it's never seen before, it will try to load it because the
      class' name doesn't match any of the patterns in the default
      exclude list.  That's when a <code>LinkageError</code>
      occurs. This is really a flaw in the JUnit classloader design,
      but there is the workaround given above.
    </p>
    <p>
      Java 2 JVMs keep classes (remember, classes and objects, though
      related, are different entities to the JVM - I'm talking
      about classes here, not object instances) in namespaces,
      identifying them by their fully qualified classname plus the
      instance of their defining (not initiating) loader. The JVM will
      attempt to assign all unloaded classes referenced by an already
      defined and loaded class to that class's defining loader. The
      JVM's classresolver routine (implemented as a C function in the
      JVM source code) keeps track of all these class loading events
      and &quot;sees&quot; if another classloader (such as the JUnit
      custom loader) attempts to define a class that has already been
      defined by the system loader. According to the rules of Java 2
      loader constraints, in case a class has already been defined by
      the system loader, any attempts to load a class should first be
      delegated to the system loader. A &quot;proper&quot; way for
      JUnit to handle this feature would be to load classes from a
      repository other than the CLASSPATH that the system classloader
      knows nothing about. And then the JUnit custom classloader could
      follow the standard Java 2 delegation model, which is to always
      delegate class loading to the system loader, and only attempt to
      load if that fails. Since they both load from the CLASSPATH in
      the current model, if the JUnit loader delegated like it's
      supposed to, it would never get to load any classes since the
      system loader would always find them.
    </p>
    <p>
      You could try to hack around this in the JUnit source by
      catching the <code>LinkageError</code> in
      TestCaseClassLoader's <code>loadClass()</code> method and then
      making a recovery call to <code>findSystemClass()</code> --
      thereby delegating to the system loader after the violation has
      been caught. But this hack only works some of the time, because
      now you can have the reverse problem where the JUnit loader will
      load a host of <code>org.w3c.dom</code>/<code>org.xml.sax</code>
      classes, and then the system loader violates the loader
      contraints at some point when it tries to do exactly what I
      described above with JAXP because it doesn't ever delegate to
      its logical child (the JUnit loader). Inevitably, if your test
      cases use many JAXP and related XML classes, one or the other
      classloader will end up violating the constraints whatever you
      do.
    </p></answer>
        </faq>
        <faq id="running_11">
            <question>Why do I get the warning
      "AssertionFailedError: No
        tests found in XXX" when I run my test?</question>
            <answer><p>
      Make sure you have more or more method annotated with <code>@Test</code>.
    </p>
    <p>
      For example:
    </p>
<pre class="prettyprint linenums">@Test
public void testSomething() {
}</pre></answer>
        </faq>
        <faq id="running_12">
            <question>Why do I see "Unknown Source" in the
      stack trace of
a test failure, rather than the source file's line number?</question>
            <answer><p>
      The debug option for the Java compiler must be enabled in order
      to see source file and line number information in a stack trace.
    </p>
    <p>
      When invoking the Java compiler from the command line, use
      the <code>-g</code> option to generate all debugging info.
    </p>
    <p>
      When invoking the Java compiler from an 
      <a href="http://jakarta.apache.org/ant/index.html">Ant</a> task, use the
      <code>debug="on"</code> attribute.  For example:
    </p>
      <pre>&lt;javac srcdir="${src}" destdir="${build}" debug="on" /&gt;</pre>
    <p>
      When using older JVMs pre-Hotspot (JDK 1.1 and most/all 1.2),
      run JUnit with the <code>-DJAVA_COMPILER=none</code> JMV command
      line argument to prevent runtime JIT compilation from obscuring
      line number info.
    </p>
    <p>
      Compiling the test source with debug enabled will show the line
      where the assertion failed.  Compiling the non-test source with
      debug enabled will show the line where an exception was raised
      in the class under test.
    </p></answer>
        </faq>
        <faq id="running_15">
            <question>How do I organize all test classes
        in a TestSuite automatically and not use or manage a TestSuite
        explicitly?</question>
            <answer><p>
      <i>(Submitted by: Bill de hora)</i>
    </p>
    <p>
      There are a number of ways to do this:
    </p>
    <ol>
      <li>
        <p>
          In Ant, use the <code>junit</code> task and
          the <code>batchtest</code> element:
        </p>
        <div>
          <pre class="prettyprint linenums">
&lt;junit printsummary="yes" haltonfailure="yes"&gt;
  ...
  &lt;batchtest fork="yes"&gt;
    &lt;fileset dir="${src.dir}"&gt;
       &lt;include name="**/*Test.java" /&gt;
       &lt;include name="**/Test*.java" /&gt;
    &lt;/fileset&gt;
  &lt;/batchtest&gt;
&lt;/junit&gt; 
          </pre>
        </div>
        <p>
          Idiomatic naming patterns for unit tests
          are <code>Test*.java</code> and <code>*Test.java</code>.
          Documentation and examples are at <a
                                               href="http://ant.apache.org/manual/OptionalTasks/junit.html">http://ant.apache.org/manual/OptionalTasks/junit.html</a>.
        </p>
      </li>
      <li>
        <p>
          Use the <code>DirectorySuiteBuilder</code>
          and <code>ArchiveSuiteBuilder</code> (for jar/zip files)
          classes provided by JUnit-addons project:
        </p>
<pre class="prettyprint linenums">DirectorySuiteBuilder builder = new DirectorySuiteBuilder();
builder.setSuffix("Test");
Test suite = builer.suite("/home/project/myproject/tests");</pre>
        <p>
          Documentation and examples are at <a
                                               href="http://junit-addons.sourceforge.net/">http://junit-addons.sourceforge.net</a>.
        </p>
      </li>
      <li>
        <p>
          Write your own custom suite builder. 
        </p>
        <p>
          Have your test classes implement an interface and write a
          treewalker to load each class in a directory, inspect the
          class, and add any classes that implement the interface to a
          TestSuite.
        </p>
        <p>
          You might only want to do this if you are <b>very</b>
          uncomfortable with using a naming convention for test
          classes. Aside from being slow for larger suites, ultimately
          it's arguable whether it's more effort to follow a naming
          convention that have test classes implement an interface!
        </p>
        <p>
          An example of this approach is at 
          <a href="http://www.javaworld.com/javaworld/jw-12-2000/jw-1221-junit_p.html">http://www.javaworld.com/javaworld/jw-12-2000/jw-1221-junit_p.html</a>.  
        </p>
    </li>
</ol>
    </answer>
        </faq>
    </part>
    <part id="best">
        <title>Best Practices</title>
        <faq id="best_1">
            <question>When should tests be written?</question>
            <answer><p>
      Tests should be written before the code.  Test-first programming
      is practiced by only writing new code when an automated test is
      failing.
    </p>
    <p>
      Good tests tell you how to best design the system for its
      intended use.  They effectively communicate in an executable
      format how to use the software.  They also prevent tendencies to
      over-build the system based on speculation.  When all the tests
      pass, you know you're done!
    </p>
    <p>
      Whenever a customer test fails or a bug is reported, first write
      the necessary unit test(s) to expose the bug(s), <em>then</em>
      fix them. This makes it almost impossible for that particular
      bug to resurface later.
    </p>
    <p>
      Test-driven development is a lot more fun than writing tests
      after the code seems to be working.  Give it a try!
    </p></answer>
        </faq>
        <faq id="best_2">
            <question>Do I have to write a test for
        everything?</question>
            <answer><p>
      No, just test everything that could reasonably break.  
    </p>
    <p>
      Be practical and maximize your testing investment.  Remember
      that investments in testing are equal investments in design.  If
      defects aren't being reported and your design responds well to
      change, then you're probably testing enough.  If you're spending
      a lot of time fixing defects and your design is difficult to
      grow, you should write more tests.
    </p>
    <p>
      If something is difficult to test, it's usually an opportunity
      for a design improvement.  Look to improve the design so that
      it's easier to test, and by doing so a better design will
      usually emerge.
    </p></answer>
        </faq>
        <faq id="best_3">
            <question>How simple is 'too simple to break'?</question>
            <answer><p>
      <i>(Submitted by: J. B. Rainsberger)</i>
    </p>
    <p>
      The general philosophy is this: if it can't break <em>on its
      own</em>, it's too simple to break.
    </p>
    <p>
      First example is the <code>getX()</code> method. Suppose
      the <code>getX()</code> method only answers the value of an
      instance variable. In that case, <code>getX()</code> cannot
      break unless either the compiler or the interpreter is also
      broken. For that reason, don't test <code>getX()</code>; there
      is no benefit.  The same is true of the <code>setX()</code>
      method, although if your <code>setX()</code> method does any
      parameter validation or has any side effects, you likely need to
      test it.
    </p>
    <p>
      Next example: suppose you have written a method that does
      nothing but forward parameters into a method called on another
      object. That method is too simple to break.
    </p>
<pre class="prettyprint linenums">public void myMethod(final int a, final String b) {
    myCollaborator.anotherMethod(a, b);
}</pre>
    <p>
      <code>myMethod</code> cannot possibly break because it does nothing: it 
      forwards its input to another object and that's all. 
    </p>
    <p>
      The only precondition for this method is "myCollaborator !=
      null", but that is generally the responsibility of the
      constructor, and not of myMethod. If you are concerned, add a
      test to verify that myCollaborator is always set to something
      non-null by every constructor.
    </p>
    <p>
      The only way myMethod could break would be
      if <code>myCollaborator.anotherMethod()</code> were broken. In
      that case, test <code>myCollaborator</code>, and not the current
      class.
    </p>
    <p>
      It is true that adding tests for even these simple methods
      guards against the possibility that someone refactors and makes
      the methods "not-so-simple" anymore. In that case, though, the
      refactorer needs to be aware that the method is now complex
      enough to break, and should write tests for it -- and preferably
      before the refactoring.
    </p>
    <p>
      Another example: suppose you have a JSP and, like a good
      programmer, you have removed all business logic from it. All it
      does is provide a layout for a number of JavaBeans and never
      does anything that could change the value of any object. That
      JSP is too simple to break, and since JSPs are notoriously
      annoying to test, you should strive to make all your JSPs too
      simple to break.
    </p>
    <p>
      Here's the way testing goes: 
    </p>
    <pre class="prettyprint linenums">becomeTimidAndTestEverything
while writingTheSameThingOverAndOverAgain
    becomeMoreAggressive
    writeFewerTests
    writeTestsForMoreInterestingCases
    if getBurnedByStupidDefect
        feelStupid
        becomeTimidAndTestEverything
    end
end</pre>
    <p>
      The loop, as you can see, never terminates.
    </p></answer>
        </faq>
        <faq id="best_4">
            <question>How often should I run my tests?</question>
            <answer><p>
      Run all your unit tests as often as possible, ideally every time
      the code is changed.  Make sure all your unit tests always run
      at 100%.  Frequent testing gives you confidence that your
      changes didn't break anything and generally lowers the stress of
      programming in the dark.
    </p>
    <p>
      For larger systems, you may just run specific test suites that
      are relevant to the code you're working on.
    </p>
    <p>
      Run all your acceptance, integration, stress, and unit tests at
      least once per day (or night).
    </p>
    <p>
      If you're using Eclipse, be sure to check out David Saff's 
      <a href="http://pag.csail.mit.edu/continuoustesting/">continuous
      testing plug-in</a>.
    </p></answer>
        </faq>
        <faq id="best_5">
            <question>What do I do when a defect is reported?</question>
            <answer><p>
      Test-driven development generally lowers the defect density of
      software.  But we're all fallible, so sometimes a defect will
      slip through.  When this happens, write a failing test that
      exposes the defect.  When the test passes, you know the defect
      is fixed!
    </p>
    <p>
      Don't forget to use this as a learning opportunity.  Perhaps the
      defect could have been prevented by being more aggressive about
      testing everything that could reasonably break.
    </p></answer>
        </faq>
        <faq id="best_6">
            <question>Why not just use <code>System.out.println()</code>?</question>
            <answer><p>
      Inserting debug statements into code is a low-tech method for
      debugging it.  It usually requires that output be scanned
      manually every time the program is run to ensure that the code
      is doing what's expected.
    </p>
    <p>
      It generally takes less time in the long run to codify
      expectations in the form of an automated JUnit test that retains
      its value over time.  If it's difficult to write a test to
      assert expectations, the tests may be telling you that shorter
      and more cohesive methods would improve your design.
    </p></answer>
        </faq>
        <faq id="best_7">
            <question>Why not just use a debugger?</question>
            <answer><p>
      Debuggers are commonly used to step through code and inspect
      that the variables along the way contain the expected values.
      But stepping through a program in a debugger is a manual process
      that requires tedious visual inspections.  In essence, the
      debugging session is nothing more than a manual check of
      expected vs. actual results.  Moreover, every time the program
      changes we must manually step back through the program in the
      debugger to ensure that nothing broke.
    </p>
    <p>
      It generally takes less time to codify expectations in the form
      of an automated JUnit test that retains its value over time.  If
      it's difficult to write a test to assert expected values, the
      tests may be telling you that shorter and more cohesive methods
      would improve your design.
    </p></answer>
        </faq>
   </part>
    <part id="misc">
        <title>Miscellaneous</title>
        <faq id="misc_1">
            <question>How do I integrate JUnit with my IDE?</question>
            <answer><p>
      The JUnit home page maintains a list of <a
      href="http://www.junit.org/news/ide/index.htm">IDE integration
      instructions</a>.
    </p></answer>
        </faq>
        <faq id="misc_2">
            <question>How do I launch a debugger when a test fails?</question>
            <answer>    <p>
      Start the <code>TestRunner</code> under the debugger and
      configure the debugger so that it catches
      the <code>junit.framework.AssertionFailedError</code>.
    </p>
    <p>
      How you configure this depends on the debugger you prefer to
      use. Most Java debuggers provide support to stop the program
      when a specific exception is raised.
    </p>
    <p>
      Notice that this will only launch the debugger when an expected
      failure occurs.
    </p></answer>
        </faq>
        <faq id="misc_3">
            <question>Where can I find unit testing frameworks
      similar to JUnit for other languages?</question>
            <answer><p>
      XProgramming.com maintains a complete list of available <a
      href="http://www.xprogramming.com/software.htm">xUnit testing
      frameworks</a>.
    </p></answer>
        </faq>
    </part>
</faqs>