From a given set of test classes, the Categories runner runs only the classes and methods that are annotated with either the category given with the @IncludeCategory annotation, or a subtype of that category. Either classes or interfaces can be used as categories. Subtyping works, so if you say @IncludeCategory(SuperClass.class), a test marked @Category({SubClass.class}) will be run.

You can also exclude categories by using the @ExcludeCategory annotation

Example:

public interface FastTests { /* category marker */ }
public interface SlowTests { /* category marker */ }

public class A {
  @Test
  public void a() {
    fail();
  }

  @Category(SlowTests.class)
  @Test
  public void b() {
  }
}

@Category({SlowTests.class, FastTests.class})
public class B {
  @Test
  public void c() {

  }
}

@RunWith(Categories.class)
@IncludeCategory(SlowTests.class)
@SuiteClasses( { A.class, B.class }) // Note that Categories is a kind of Suite
public class SlowTestSuite {
  // Will run A.b and B.c, but not A.a
}

@RunWith(Categories.class)
@IncludeCategory(SlowTests.class)
@ExcludeCategory(FastTests.class)
@SuiteClasses( { A.class, B.class }) // Note that Categories is a kind of Suite
public class SlowTestSuite {
  // Will run A.b, but not A.a or B.c
}

You can use categories with either maven-surefire-plugin (for unit tests) or maven-failsafe-plugin (for integration tests). Using either plugin, you can configure a list of categories to include or exclude. Without using either option, all tests will be executed by default.

<build>
  <plugins>
    <plugin>
      <artifactId>maven-surefire-pluginartifactId>
      <configuration>
        <groups>com.example.FastTests,com.example.RegressionTestsgroups>
      configuration>
    plugin>
  plugins>
build>

Similarly, to exclude a certain list of categories, you would use the configuration element.

Gradle's test task allows the specification of the JUnit categories you want to include and exclude.

test {
    useJUnit {
        includeCategories 'org.gradle.junit.CategoryA'
        excludeCategories 'org.gradle.junit.CategoryB'
    }
}

SBT's junit-interface allows the specification of JUnit categories via --include-categories= and --exclude-categories=.

Categories are used to add metadata on the tests.

The frequently encountered categories usages are about:

• The type of automated tests: UnitTests, IntegrationTests, SmokeTests, RegressionTests, PerformanceTests ...
• How quick the tests execute: SlowTests, QuickTests
• In which part of the ci build the tests should be executed: NightlyBuildTests
• The state of the test: UnstableTests, InProgressTests

This is also used to add project specific metadata like which feature of a project is covered by the test.

See usages of Junit Categories on github hosted projects