Tutorial :Changing names of parameterized tests


Is there a way to set my own custom test case names when using parameterized tests in JUnit4?

I'd like to change the default â€" [Test class].runTest[n] â€" to something meaningful.


This feature has made it into JUnit 4.11.

To use change the name of parameterized tests, you say:


namestring is a string, which can have the following special placeholders:

  • {index} - the index of this set of arguments. The default namestring is {index}.
  • {0} - the first parameter value from this invocation of the test.
  • {1} - the second parameter value
  • and so on

The final name of the test will be the name of the test method, followed by the namestring in brackets, as shown below.

For example (adapted from the unit test for the Parameterized annotation):

@RunWith(Parameterized.class)  static public class FibonacciTest {        @Parameters( name = "{index}: fib({0})={1}" )      public static Iterable<Object[]> data() {          return Arrays.asList(new Object[][] { { 0, 0 }, { 1, 1 }, { 2, 1 },                  { 3, 2 }, { 4, 3 }, { 5, 5 }, { 6, 8 } });      }        private final int fInput;      private final int fExpected;        public FibonacciTest(int input, int expected) {          fInput= input;          fExpected= expected;      }        @Test      public void testFib() {          assertEquals(fExpected, fib(fInput));      }        private int fib(int x) {          // TODO: actually calculate Fibonacci numbers          return 0;      }  }  

will give names like testFib[1: fib(1)=1] and testFib[4: fib(4)=3]. (The testFib part of the name is the method name of the @Test).


Looking at JUnit 4.5, its runner clearly doesn't support that, as that logic is buried inside a private class inside the Parameterized class. You could not use the JUnit Parameterized runner, and create your own instead which would understand the concept of names (which leads to the question of how you might set a name ...).

From a JUnit perspective, it would be nice if instead of (or in addition to) just passing an increment, they would pass the comma delimited arguments. TestNG does this. If the feature is important to you, you can comment on the yahoo mailing list referenced at www.junit.org.


I recently came across the same problem when using JUnit 4.3.1. I implemented a new class which extends Parameterized called LabelledParameterized. It has been tested using JUnit 4.3.1, 4.4 and 4.5. It reconstructs the Description instance using the String representation of the first argument of each parameter array from the @Parameters method. You can see the code for this at:


and an example of its use at:


The test description formats nicely in Eclipse which is what I wanted since this makes failed tests a lot easier to find! I will probably further refine and document the classes over the next few days/weeks. Drop the '?' part of the URLs if you want the bleeding edge. :-)

To use it, all you have to do is copy that class (GPL v3), and change @RunWith(Parameterized.class) to @RunWith(LabelledParameterized.class) assuming the first element of your parameter list is a sensible label.

I don't know if any later releases of JUnit address this issue but even if they did, I can't update JUnit since all my co-developers would have to update too and we have higher priorities than re-tooling. Hence the work in the class to be compilable by multiple versions of JUnit.

Note: there is some reflection jiggery-pokery so that it runs across the different JUnit versions as listed above. The version specifically for JUnit 4.3.1 can be found here and, for JUnit 4.4 and 4.5, here.


With Parameterized as a model, I wrote my own custom test runner / suite -- only took about half an hour. It's slightly different from darrenp's LabelledParameterized in that it lets you specify a name explicitly rather than relying on the first parameter's toString().

It also doesn't use arrays because I hate arrays. :)

public class PolySuite extends Suite {      // //////////////////////////////    // Public helper interfaces      /**     * Annotation for a method which returns a {@link Configuration}     * to be injected into the test class constructor     */    @Retention(RetentionPolicy.RUNTIME)    @Target(ElementType.METHOD)    public static @interface Config {    }      public static interface Configuration {      int size();      Object getTestValue(int index);      String getTestName(int index);    }      // //////////////////////////////    // Fields      private final List<Runner> runners;      // //////////////////////////////    // Constructor      /**     * Only called reflectively. Do not use programmatically.     * @param c the test class     * @throws Throwable if something bad happens     */    public PolySuite(Class<?> c) throws Throwable {      super(c, Collections.<Runner>emptyList());      TestClass testClass = getTestClass();      Class<?> jTestClass = testClass.getJavaClass();      Configuration configuration = getConfiguration(testClass);      List<Runner> runners = new ArrayList<Runner>();      for (int i = 0, size = configuration.size(); i < size; i++) {        SingleRunner runner = new SingleRunner(jTestClass, configuration.getTestValue(i), configuration.getTestName(i));        runners.add(runner);      }      this.runners = runners;    }      // //////////////////////////////    // Overrides      @Override    protected List<Runner> getChildren() {      return runners;    }      // //////////////////////////////    // Private      private Configuration getConfiguration(TestClass testClass) throws Throwable {      return (Configuration) getConfigMethod(testClass).invokeExplosively(null);    }      private FrameworkMethod getConfigMethod(TestClass testClass) {      List<FrameworkMethod> methods = testClass.getAnnotatedMethods(Config.class);      if (methods.isEmpty()) {        throw new IllegalStateException("@" + Config.class.getSimpleName() + " method not found");      }      if (methods.size() > 1) {        throw new IllegalStateException("Too many @" + Config.class.getSimpleName() + " methods");      }      FrameworkMethod method = methods.get(0);      int modifiers = method.getMethod().getModifiers();      if (!(Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))) {        throw new IllegalStateException("@" + Config.class.getSimpleName() + " method \"" + method.getName() + "\" must be public static");      }      return method;    }      // //////////////////////////////    // Helper classes      private static class SingleRunner extends BlockJUnit4ClassRunner {        private final Object testVal;      private final String testName;        SingleRunner(Class<?> testClass, Object testVal, String testName) throws InitializationError {        super(testClass);        this.testVal = testVal;        this.testName = testName;      }        @Override      protected Object createTest() throws Exception {        return getTestClass().getOnlyConstructor().newInstance(testVal);      }        @Override      protected String getName() {        return testName;      }        @Override      protected String testName(FrameworkMethod method) {        return testName + ": " + method.getName();      }        @Override      protected void validateConstructor(List<Throwable> errors) {        validateOnlyOneConstructor(errors);      }        @Override      protected Statement classBlock(RunNotifier notifier) {        return childrenInvoker(notifier);      }    }  }  

And an example:

@RunWith(PolySuite.class)  public class PolySuiteExample {      // //////////////////////////////    // Fixture      @Config    public static Configuration getConfig() {      return new Configuration() {        @Override        public int size() {          return 10;        }          @Override        public Integer getTestValue(int index) {          return index * 2;        }          @Override        public String getTestName(int index) {          return "test" + index;        }      };    }      // //////////////////////////////    // Fields      private final int testVal;      // //////////////////////////////    // Constructor      public PolySuiteExample(int testVal) {      this.testVal = testVal;    }      // //////////////////////////////    // Test      @Ignore    @Test    public void odd() {      assertFalse(testVal % 2 == 0);    }      @Test    public void even() {      assertTrue(testVal % 2 == 0);    }    }  


from junit4.8.2, you can create your own MyParameterized class by simply copy Parameterized class. change the getName() and testName() methods in TestClassRunnerForParameters.


You may also want to try JUnitParams: http://code.google.com/p/junitparams/


You can create a method like

@Test  public void name() {      Assert.assertEquals("", inboundFileName);  }  

While I wouldn't use it all the time it would be useful to figure out exactly which test number 143 is.


I make extensive use of static import for Assert and friends, so it is easy for me to redefine assertion:

private <T> void assertThat(final T actual, final Matcher<T> expected) {      Assert.assertThat(editThisToDisplaySomethingForYourDatum, actual, expected);  }  

For example, you could add a "name" field to your test class, initialized in the constructor, and display that on test failure. Just pass it in as the first elements of your parameters array for each test. This also helps label the data:

public ExampleTest(final String testLabel, final int one, final int two) {      this.testLabel = testLabel;      // ...  }    @Parameters  public static Collection<Object[]> data() {      return asList(new Object[][]{          {"first test", 3, 4},          {"second test", 5, 6}      });  }  


None of it was working for me, so I got the source for Parameterized and modified it create a a new test runner. I didn't have to change much but IT WORKS!!!

import java.lang.annotation.ElementType;  import java.lang.annotation.Retention;  import java.lang.annotation.RetentionPolicy;  import java.lang.annotation.Target;  import java.lang.reflect.Constructor;  import java.lang.reflect.InvocationTargetException;  import java.lang.reflect.Method;  import java.lang.reflect.Modifier;  import java.util.ArrayList;  import java.util.Arrays;  import java.util.Collection;  import java.util.List;  import org.junit.Assert;  import org.junit.internal.runners.ClassRoadie;  import org.junit.internal.runners.CompositeRunner;  import org.junit.internal.runners.InitializationError;  import org.junit.internal.runners.JUnit4ClassRunner;  import org.junit.internal.runners.MethodValidator;  import org.junit.internal.runners.TestClass;  import org.junit.runner.notification.RunNotifier;    public class LabelledParameterized extends CompositeRunner {  static class TestClassRunnerForParameters extends JUnit4ClassRunner {      private final Object[] fParameters;        private final String fParameterFirstValue;        private final Constructor<?> fConstructor;        TestClassRunnerForParameters(TestClass testClass, Object[] parameters, int i) throws InitializationError {          super(testClass.getJavaClass()); // todo          fParameters = parameters;          if (parameters != null) {              fParameterFirstValue = Arrays.asList(parameters).toString();          } else {              fParameterFirstValue = String.valueOf(i);          }          fConstructor = getOnlyConstructor();      }        @Override      protected Object createTest() throws Exception {          return fConstructor.newInstance(fParameters);      }        @Override      protected String getName() {          return String.format("%s", fParameterFirstValue);      }        @Override      protected String testName(final Method method) {          return String.format("%s%s", method.getName(), fParameterFirstValue);      }        private Constructor<?> getOnlyConstructor() {          Constructor<?>[] constructors = getTestClass().getJavaClass().getConstructors();          Assert.assertEquals(1, constructors.length);          return constructors[0];      }        @Override      protected void validate() throws InitializationError {          // do nothing: validated before.      }        @Override      public void run(RunNotifier notifier) {          runMethods(notifier);      }  }    @Retention(RetentionPolicy.RUNTIME)  @Target(ElementType.METHOD)  public static @interface Parameters {  }    private final TestClass fTestClass;    public LabelledParameterized(Class<?> klass) throws Exception {      super(klass.getName());      fTestClass = new TestClass(klass);        MethodValidator methodValidator = new MethodValidator(fTestClass);      methodValidator.validateStaticMethods();      methodValidator.validateInstanceMethods();      methodValidator.assertValid();        int i = 0;      for (final Object each : getParametersList()) {          if (each instanceof Object[])              add(new TestClassRunnerForParameters(fTestClass, (Object[]) each, i++));          else              throw new Exception(String.format("%s.%s() must return a Collection of arrays.", fTestClass.getName(), getParametersMethod().getName()));      }  }    @Override  public void run(final RunNotifier notifier) {      new ClassRoadie(notifier, fTestClass, getDescription(), new Runnable() {          public void run() {              runChildren(notifier);          }      }).runProtected();  }    private Collection<?> getParametersList() throws IllegalAccessException, InvocationTargetException, Exception {      return (Collection<?>) getParametersMethod().invoke(null);  }    private Method getParametersMethod() throws Exception {      List<Method> methods = fTestClass.getAnnotatedMethods(Parameters.class);      for (Method each : methods) {          int modifiers = each.getModifiers();          if (Modifier.isStatic(modifiers) && Modifier.isPublic(modifiers))              return each;      }        throw new Exception("No public static parameters method on class " + getName());  }    public static Collection<Object[]> eachOne(Object... params) {      List<Object[]> results = new ArrayList<Object[]>();      for (Object param : params)          results.add(new Object[] { param });      return results;  }  }  


A workaround would be to catch and nest all Throwables into a new Throwable with a custom message that contains all information about the parameters. The message would appear in the stack trace. This works whenever a test fails for all assertions, errors and exceptions as they are all subclasses of Throwable.

My code looks like this:

@RunWith(Parameterized.class)  public class ParameterizedTest {        int parameter;        public ParameterizedTest(int parameter) {          super();          this.parameter = parameter;      }        @Parameters      public static Collection<Object[]> data() {          return Arrays.asList(new Object[][] { {1}, {2} });      }        @Test      public void test() throws Throwable {          try {              assertTrue(parameter%2==0);          }          catch(Throwable thrown) {              throw new Throwable("parameter="+parameter, thrown);          }      }    }  

The stack trace of the failed test is:

java.lang.Throwable: parameter=1      at sample.ParameterizedTest.test(ParameterizedTest.java:34)  Caused by: java.lang.AssertionError      at org.junit.Assert.fail(Assert.java:92)      at org.junit.Assert.assertTrue(Assert.java:43)      at org.junit.Assert.assertTrue(Assert.java:54)      at sample.ParameterizedTest.test(ParameterizedTest.java:31)      ... 31 more  


Check out JUnitParams as dsaff mentioned, works using ant to build parameterized test method descriptions in the html report.

This was after trying LabelledParameterized and finding that it although it works with eclipse it does not work with ant as far as the html report is concerned.



Since the parameter accessed (e.g. with "{0}" always returns the toString() representation, one workaround would be to make an anonymous implementation and override toString() in each case. For example:

public static Iterable<? extends Object> data() {      return Arrays.asList(          new MyObject(myParams...) {public String toString(){return "my custom test name";}},          new MyObject(myParams...) {public String toString(){return "my other custom test name";}},          //etc...      );  }  

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