Generating display names for @ParameterizedTest in JUnit 5

Question

I have a bunch of @ParameterizedTests that receive parameters from a @MethodSource with quite verbose toString() results (e.g. Selenium's WebDriver). These are used per default to compose the corresponding display names. From the JUnit 5 user guide:

By default, the display name of a parameterized test invocation contains the invocation index and the String representation of all arguments for that specific invocation. However, you can customize invocation display names via the name attribute of the @ParameterizedTest annotation […]

While this allows customizing the display names to a certain degree, it seems like I cannot adapt the string representation of the individual parameters. Unfortunately, specifying a generator via @DisplayNameGeneration can only be applied at the class level and doesn't affect the display name of the parameterized test invocations.

Is there a way to use a DisplayNameGenerator for @ParameterizedTest or to customize the string representation of the given parameters?

Answer 1

As of JUnit 5.8.0, there is a Named<T> interface as part of the JUnit Jupiter API with "automatic support for injecting the contained payload [the arguments] into parameterized methods directly" (see issue #2301). Example:

@DisplayName("A parameterized test with named arguments")
@ParameterizedTest
@MethodSource("namedArguments")
void testWithNamedArguments(File file) {}

static Stream<Arguments> namedArguments() {
    return Stream.of(
        Arguments.of(Named.of("An important file", new File("path1"))),
        Arguments.of(Named.of("Another file", new File("path2")))
    );
}

If you prefer static imports, you can also go for the corresponding aliases from Arguments and Named:

arguments(named("An important file", new File("path1")))

JUnit 5.11.0 also allows to provide a name for an entire set of arguments:

argumentSet("Important files", new File("path1"), new File("path2"))

For more information, please refer to the corresponding docs.