Junit @RunWith(Parameterized.class)

Question

The differences between the following 2 cases are

a> The type of variable 'arr'. In the first case, its type is Integer[], while in the second case its type is int[].

b> We can see from where I marked as "// here" that in the case 1 it needs Integer[][][]. while in the case 2 it needs int[][].

Both of case 1 and case 2 work. So my question comes:

Why Junit require I return a 3-dimentional Integer array in the data() method in case 1 when the test data is a 1-dimentional Integer array. I expected it should be 2 - dimentional Integer array because in the case 2 I return a 2 - dimentional int array in the data() method and it is easy to understand it and it works. But when I tried to return 2-dimentional Integer array in the data() method in case 1 as

    @Parameterized.Parameters(name = "test with {index}")
    public static Iterable<Integer[]> data() {
      return Arrays.asList(new Integer[][]{ 
            {3, 1, 4, 6, 7, 9},  
            {9, 8, 7, 6, 5, 4},  
      }); 
    }

Junit reported "java.lang.IllegalArgumentException: wrong number of arguments". Please help me if you know the reason.

I searched Junit documents and many other pages without satisfied answer. Please help.My Junit version is 4.12.

case 1

@RunWith(Parameterized.class)
public class MyTest {
    @Parameterized.Parameters(name = "test with {index}")
    public static Iterable<Integer[][]> data() {
      //here:  My question is why it can not be Integer[][]
      return Arrays.asList(new Integer[][][]{ 
            {{3, 1, 4, 6, 7, 9}},  
            {{9, 8, 7, 6, 5, 4}},  
      }); 
    }

    private Integer[] arr;

    public MyTest(Integer[] arr) {
      this.arr = arr;
    }
    public methodTest(int[] arr) {
     // ignore the code here 
    }
}

case 2

@RunWith(Parameterized.class)
public class MyTest {
  @Parameterized.Parameters(name = "test with {index}")
  public static Iterable<int[]> data() {
    //here int[][] works 
    return Arrays.asList(new int[][]{ 
            {3, 1, 4, 6, 7, 9},  
            {9, 8, 7, 6, 5, 4},  
  }

  private int[] arr;

  public  MyTest(int[] arr) {
    this.arr = arr;
  }

  public methodTest(int[] arr) {
    // ignore the code here 
  }
}

It's not clear what is your problem. Would you mind adding some comments about expected and actual results on each of these cases? Minimal complete example which demonstrates the problem would also be useful. — yeputons
– yeputons, Commented May 14, 2016 at 19:53
Do you have @RunWith(Parameterized.class) annotation before both of your test classes? — yeputons
– yeputons, Commented May 14, 2016 at 20:17
So, again, what's your problem? Do any of these test cases do what you expect? Is having a private field essential for reproducing the problem? What version of JUnit do you use? I'm a little worried about the extra parameter that you pass to testing methods - testing methods should not take any parameters, because JUnit creates a new test class instance for each parameter, which is passed into constructor only — yeputons
– yeputons, Commented May 14, 2016 at 21:35

timbre timbre · Accepted Answer · 2016-05-14 23:12:06Z

Data itself should always be the same type as data expected by constructor, not by test. Also you've got a bit lost between structure of data() and the data itself. I prefer the following structure, it clearly expresses what we need:

@Parameters
public static Collection<Object[]> data() 
{
    return Arrays.asList(
        new Object[][] 
        { 
            {/* case 1*/},
            {/* case 2*/},
        }
    );
}

Maybe this is not the shortest way, but you will never get lost with it, even with complex data. Every line here, except for /* case 1*/ and /* case 1*/ never changes. On top level we have a collection of arrays (of type object) and we create this collection by providing a 2-dimentional array of objects, with each row expressing test case.

So your Case 1 will become

@Parameterized.Parameters(name = "test with {index}")
public static Collection<Object[]> data() {
    return Arrays.asList(
        new Object[][] 
        { 
            {new Integer[]{3, 1, 4, 6, 7, 9}}, // here
            {new Integer[]{9, 8, 7, 6, 5, 4}}, // here
        }
    );
}

and Case 2 will become

@Parameterized.Parameters(name = "test with {index}")
public static Collection<Object[]> data() {
    return Arrays.asList(
        new Object[][] 
        { 
            {new int[]{3, 1, 4, 6, 7, 9}}, // here
            {new int[]{9, 8, 7, 6, 5, 4}}, // here
        }
    );
}

You also need to fix a couple of other problematic lines in your code, e.g. lack of return type on the test. Here's an example of complete runnable and passing test:

package x;

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

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

@RunWith(Parameterized.class)
public class MyTest 
{
    @Parameterized.Parameters(name = "test with {index}")
    public static Collection<Object[]> data() {
        return Arrays.asList(
                new Object[][] 
                { 
                    {new Integer[]{3, 1, 4, 6, 7, 9}}, // here
                    {new Integer[]{9, 8, 7, 6, 5, 4}}, // here
      });
    }

    private Integer[] arr;

    public MyTest(Integer[] arr) {
      this.arr = arr;
    }

    @Test
    public void methodTest() {
     // test some logic
        System.out.println(arr.length);
    }
}

Hi Kiril S. , Thank you for your help with so detail case which is really a good workaround.
@Kiril S. You don't have to convert the Object[][] array to a list: public static Object[][] data() ... is fine.

Hank D · Accepted Answer · 2016-05-14 23:45:52Z

0

The reason your Integer version requires more dimensions than the int version is that the first Iterable is Iterable<Integer [][]> which has one more dimension than the second one, Iterable<int[]>.

answered May 14, 2016 at 23:45

Hank D

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