 ------
 Using JUnit
 ------
 Kristian Rosenvold <krosenvold@apache.org>
 ------
 2010-10-10
 ------
 
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 ~~
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Using JUnit

* Configuring JUnit

  To get started with JUnit, you need to add the required version of JUnit to your project:

+---+
<dependencies>
  [...]
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.13.2</version>
      <scope>test</scope>
    </dependency>
  [...]
</dependencies>
+---+


  This is the only step that is required to get started - you can now create tests in your test source directory
  (e.g., <<<src/test/java>>>).

* Different Generations of JUnit support

  Surefire supports three different generations of JUnit: JUnit 3.8.x, JUnit 4.x (serial provider) and JUnit 4.7 (junit-core provider
  with parallel support). The provider is selected based on the JUnit version in your project and the configuration parameters (for parallel).

* Upgrade Check for JUnit 4.x

  As of Surefire version 2.7, the algorithm for choosing which tests to run
  has changed. From 2.7 and on, only valid JUnit tests are run for all versions of JUnit, where older versions
  of the plugin would also run invalid tests that satisfied the naming convention.

  When upgrading from a Surefire version prior to 2.7, the build can be run with
  the flag <<<-Dsurefire.junit4.upgradecheck>>>. This will perform a check and notify you of any invalid tests that
  will not be run with this version of Surefire (and the build fails). This is only meant to be used as a tool
  when upgrading to check that all expected tests will be run. It is a transitional
  feature that will be removed in a future version of surefire.

* Provider Selection

   If nothing is configured, Surefire detects which JUnit version to use by the following algorithm:

+---+
if the JUnit 5 Platform Engine is present in the project
    use junit-platform
if the JUnit version in the project >= 4.7 and the <<<parallel>>> configuration parameter has ANY value
    use junit47 provider
if JUnit >= 4.0 is present
    use junit4 provider
else
    use junit3.8.1
+---+

    Please note that the "else" part of this algorithm is also a FAQ response:

    You depend on the appropriate version of JUnit being present in the project dependencies, or Surefire may choose the wrong
    provider. If, for instance, one of your dependencies pulls in JUnit 3.8.1 you risk that surefire chooses the
    3.8.1 provider, which will not support annotations or any of the 4.x features.

    Use <<<mvn dependency:tree>>>, POM dependency ordering and/or exclusion of transitive dependencies to fix this problem.

** Manually Specifying a Provider

   You can also manually force a specific provider by adding it as a dependency to ${thisPlugin} itself:

+---+
<plugins>
[...]
  <plugin>
    <groupId>${project.groupId}</groupId>
    <artifactId>${project.artifactId}</artifactId>
    <version>${project.version}</version>
    <dependencies>
      <dependency>
        <groupId>org.apache.maven.surefire</groupId>
        <artifactId>surefire-junit47</artifactId>
        <version>${project.version}</version>
      </dependency>
    </dependencies>
  </plugin>
[...]
</plugins>
+---+

  When using this technique there  is no check that the proper test-frameworks are present on your project's
  classpath. Failing to add the proper test-frameworks will result in a build failure.

* Running Tests in Parallel

  From JUnit 4.7 onwards you can run your tests in parallel. To do this, you must set the
  <<<parallel>>> parameter, and may change the <<<threadCount>>> or <<<useUnlimitedThreads>>> attribute.
  For example:

+---+
<plugins>
    [...]
      <plugin>
        <groupId>${project.groupId}</groupId>
        <artifactId>${project.artifactId}</artifactId>
        <version>${project.version}</version>
        <configuration>
          <parallel>methods</parallel>
          <threadCount>10</threadCount>
        </configuration>
      </plugin>
    [...]
</plugins>
+---+


  If your tests specify any value for the <<<parallel>>> attribute and your project uses JUnit 4.7+, your request will be routed to
  the concurrent JUnit provider, which uses the JUnit JUnitCore test runner.

  This is particularly useful for slow tests that can have high concurrency.

  As of Surefire 2.7, no additional dependencies are needed to use the full set of options with parallel.
  As of Surefire 2.16, new thread-count attributes are introduced, namely <<<threadCountSuites>>>, <<<threadCountClasses>>> and
  <<<threadCountMethods>>>. Additionally, the new attributes <<<parallelTestsTimeoutInSeconds>>> and
  <<<parallelTestsTimeoutForcedInSeconds>>> are used to shut down the parallel execution after an elapsed timeout, and
  the attribute <<<parallel>>> specifies new values.
  
  See also {{{./fork-options-and-parallel-execution.html}Fork Options and Parallel Test Execution}}.

* Using Custom Listeners and Reporters

  The junit4 and junit47 providers provide support for attaching custom <<<RunListeners>>> to your tests.

  You can configure multiple custom listeners like this:

+---+
<dependencies>
[...]
  <dependency>
    <groupId>your-junit-listener-artifact-groupid</groupId>
    <artifactId>your-junit-listener-artifact-artifactid</artifactId>
    <version>your-junit-listener-artifact-version</version>
    <scope>test</scope>
  </dependency>
[...]
</dependencies>
[...]
<plugins>
[...]
  <plugin>
    <groupId>${project.groupId}</groupId>
    <artifactId>${project.artifactId}</artifactId>
    <version>${project.version}</version>
    <configuration>
      <properties>
        <property>
          <name>listener</name>
          <value>com.mycompany.MyResultListener,com.mycompany.MyResultListener2</value>
        </property>
      </properties>
    </configuration>
  </plugin>
[...]
</plugins>
+---+

  For more information on JUnit, see the {{{http://www.junit.org}JUnit web site}}.

  You can implement JUnit listener interface <<<org.junit.runner.notification.RunListener>>> in
  a separate test artifact <<<your-junit-listener-artifact>>> with scope=test, or in project test source code
  <<<src/test/java>>>. You can filter test artifacts by the parameter <<<dependenciesToScan>>> to load its classes
  in current ClassLoader of surefire-junit* providers.

  Since JUnit 4.12 thread safe listener class should be annotated by
  <<<org.junit.runner.notification.RunListener.ThreadSafe>>> which avoids unnecessary locks in JUnit.


* Using a Security Manager (JUnit3 only)

   As long as <<<forkCount>>> is not 0 and you use JUnit3, you can run your tests with a Java security manager enabled.
   The class name of the security manager must be sent as a system property variable to the JUnit3 provider.

   The JDK 17 deprecated the class <<<java.lang.SecurityManager>>> and the security manager is not fully supported
   since JDK 18. The JUnit3 provider fails with enabled system property <<surefire.security.manager>>> in JDK 18+.

   JUnit4 uses mechanisms internally that are not compatible with the tested
   security managers and thus this means of configuring a security manager with JUnit4 is not supported
   by Surefire.

+---+
<plugins>
[...]
      <plugin>
        <groupId>${project.groupId}</groupId>
        <artifactId>${project.artifactId}</artifactId>
        <version>${project.version}</version>
        <configuration>
          <systemPropertyVariables>
            <surefire.security.manager>java.lang.SecurityManager</surefire.security.manager>
          </systemPropertyVariables>
        </configuration>
      </plugin>
[...]
</plugins>
+---+

* Using a Security Manager (All providers)

    Alternatively you can define a policy file that allows all providers to run with Surefire
    and configure it using the <<<argLine>>> parameter and two system properties:

+---+
<plugins>
[...]
      <plugin>
        <groupId>${project.groupId}</groupId>
        <artifactId>${project.artifactId}</artifactId>
        <version>${project.version}</version>
        <configuration>
          <argLine>-Djava.security.manager -Djava.security.policy=${basedir}/src/test/resources/java.policy</argLine>
        </configuration>
      </plugin>
[...]
</plugins>
+---+

  The disadvantage of this solution is that the policy changes will affect the tests too, which make the
  security environment less realistic.

* Using JUnit Categories

    JUnit 4.8 introduced the notion of Categories. You can use JUnit categories by using the <<<groups>>> parameter. As long as 
    the JUnit version in the project is 4.8 or higher, the presence of the "groups" parameter will automatically make Surefire select
    the junit47 provider, which supports groups.

+---+
<plugins>
[...]
    <plugin>
        <groupId>${project.groupId}</groupId>
        <artifactId>${project.artifactId}</artifactId>
        <version>${project.version}</version>
        <configuration>
            <groups>com.mycompany.SlowTests</groups>
        </configuration>
    </plugin>
[...]
</plugins>
+---+

  This will execute only those tests annotated with the <<<@Category(com.mycompany.SlowTests.class)>>> annotation and those tests
  annotated with <<<@Category(com.mycompany.SlowerTests.class)>>> if class/interface <<<SlowerTests>>> is subclass of <<<SlowTests>>>:

+---+
    public interface SlowTests{}
    public interface SlowerTests extends SlowTests{}
+---+

+---+
    public class AppTest {
      @Test
      @Category(com.mycompany.SlowTests.class)
      public void testSlow() {
        System.out.println("slow");
      }

      @Test
      @Category(com.mycompany.SlowerTests.class)
      public void testSlower() {
        System.out.println("slower");
      }

      @Test
      @Category(com.mycompany.FastTests.class)
      public void testSlow() {
        System.out.println("fast");
      }
    }
+---+

  The <<<@Category>>> annotation can also be applied at class-level.
  
  Multiple categories can be specified by comma-delimiting them in the <<<groups>>> parameter in which case tests annotated with
  any of the categories will be executed.
	
  For more information on JUnit, see the {{{http://www.junit.org}JUnit web site}}.

  Since version 2.18.1 and JUnit 4.12, the <<<@Category>>> annotation type is automatically inherited from
  superclasses, see <<<@java.lang.annotation.Inherited>>>. Make sure that test class inheritance still makes sense
  together with <<<@Category>>> annotation of the JUnit 4.12 or higher appeared in superclass.
