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JUnit 4 Tutorial

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:

import static org.junit.Assert.assertEquals;

import java.util.Arrays;
import java.util.Collection;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

@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) {
        this.fInput = input;
        this.fExpected = expected;
    }

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

public class Fibonacci {
    public static int compute(int n) {
     int result = 0;
     
        if (n <= 1) { 
         result = n; 
        } else { 
         result = compute(n - 1) + compute(n - 2); 
        }
        
        return result;
    }
}

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:

import static org.junit.Assert.assertEquals;

import java.util.Arrays;
import java.util.Collection;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameter;
import org.junit.runners.Parameterized.Parameters;

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

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

public class Fibonacci {
    ...
}

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

Tests with single parameter

(Since 4.12-beta-3)

If your test needs a single parameter only, you don't have to wrap it with an array. Instead you can provide an Iterable or an array of objects.

@Parameters
public static Iterable<? extends Object> data() {
    return Arrays.asList("first test", "second test");
}

@Parameters
public static Object[] data() {
    return new Object[] { "first test", "second test" };
}

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. NOTE: single quotes ' should be escaped as two single quotes ''.

Example

import static org.junit.Assert.assertEquals;

import java.util.Arrays;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.junit.runners.Parameterized;
import org.junit.runners.Parameterized.Parameters;

@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));
    }
}

public class Fibonacci {
    ...
}

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