Parameterized tests

The custom runner Parameterized implements parameterized tests. When running a parameterized test class, instances are created for the cross-product of the test methods and the test data elements.

For example, to test a Fibonacci function, write:

@RunWith(Parameterized.class)
public class FibonacciTest {
    @Parameters
    public static Collection<Object[]> data() {
        return Arrays.asList(new Object[][] {     
                 { 0, 0 }, { 1, 1 }, { 2, 1 }, { 3, 2 }, { 4, 3 }, { 5, 5 },{ 6, 8 }  
           });
    }

    private int fInput;

    private int fExpected;

    public FibonacciTest(int input, int expected) {
        fInput= input;
        fExpected= expected;
    }

    @Test
    public void test() {
        assertEquals(fExpected, Fibonacci.compute(fInput));
    }
}

Each instance of FibonacciTest will be constructed using the two-argument constructor and the data values in the @Parameters method.

Using @Parameter for Field injection instead of Constructor

It is also possible to inject data values directly into fields without needing a constructor using the @Parameter annotation, like so:

@RunWith(Parameterized.class)
public class FibonacciTest {
    @Parameters
    public static Collection<Object[]> data() {
        return Arrays.asList(new Object[][] {
                 { 0, 0 }, { 1, 1 }, { 2, 1 }, { 3, 2 }, { 4, 3 }, { 5, 5 },{ 6, 8 }  
           });
    }

    @Parameter // first data value (0) is default
    public /* NOT private */ int fInput;

    @Parameter(value = 1)
    public /* NOT private */ int fExpected;

    @Test
    public void test() {
        assertEquals(fExpected, Fibonacci.compute(fInput));
    }
}

This currently only works for public fields (see https://github.com/junit-team/junit/pull/737).

Identify Individual test cases

In order to easily identify the individual test cases in a Parameterized test, you may provide a name using the @Parameters annotation. This name is allowed to contain placeholders that are replaced at runtime:

• {index}: the current parameter index
• {0}, {1}, …: the first, second, and so on, parameter value

Example

@RunWith(Parameterized.class)
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 int input;
    private int expected;

    public FibonacciTest(int input, int expected) {
        this.input = input;
        this.expected = expected;
    }

    @Test
    public void test() {
        assertEquals(expected, Fibonacci.compute(input));
    }
}

In the example given above, the Parameterized runner creates names like [1: fib(3)=2]. If you don't specify a name, the current parameter index will be used by default.

IDE Bug (Eclipse)

If using the name annotation param and one of the inputs has a rounded bracket, e.g. @Parameters(name = "test({index})"), then the name gets truncated in Eclipse versions prior to 4.4 (Luna). See https://bugs.eclipse.org/bugs/show_bug.cgi?id=102512.

Before the Mars M4 release Eclipse wasn't able to run individual test subtrees, such as the ones create by the Parameterized runner. See http://blog.moritz.eysholdt.de/2014/11/new-eclipse-junit-feature-run-subtrees.html and https://bugs.eclipse.org/bugs/show_bug.cgi?id=443498.