JUnit 5: Accessing index inside ParameterizedTest

Question

Consider this snippet:

@ParameterizedTest
@ValueSource(strings = {"a", "b", "c"})
void test(final String line) {
    // code here
}

This will be an actual test, but for simplicity assume its purpose is to only print this:

Line 1: processed "a" successfully.
Line 2: processed "b" successfully.
Line 3: failed to process "c".

In other words, I want the index of the test values to be accessible within the test. From what I found, {index} can be used outside the test to name it properly.

I don't think this is possible. Why would your tests need it? — Amadán
– Amadán, Commented Jun 17, 2020 at 5:09

rieckpil · Accepted Answer · 2020-06-17 15:19:12Z

5

I am not sure if JUnit 5 currently supports this. A workaround could be to use @MethodSource and provide a List<Argument> matching your needs.

public class MyTest {

  @ParameterizedTest
  @MethodSource("methodSource")
  void test(final String input, final Integer index) {
    System.out.println(input + " " + index);
  }

  static Stream<Arguments> methodSource() {
    List<String> params = List.of("a", "b", "c");

    return IntStream.range(0, params.size())
      .mapToObj(index -> Arguments.arguments(params.get(index), index));
  }
}

edited Jun 17, 2020 at 15:19

answered Jun 17, 2020 at 5:10

rieckpil

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4 Comments

Sadeq Dousti Over a year ago

Great answer, thanks! I think we can let methodSource return Stream<Arguments>, and therefore there is no need to use .collect(Collectors.toList()) at the end. This was tested using JUnit 5.7.0-M1 successfully.

Sadeq Dousti Over a year ago

And by the way, just found a Guava method (currently in beta) which can do this: stackoverflow.com/a/42673873/459391.

rieckpil Over a year ago

you are right, this can be even simplified. I updated the answer. The Guava method looks promising

Sadeq Dousti Over a year ago

One technicality for future: Guava mapWithIndex uses Long indices rather than Integer.

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