Unit test runs only once with array as parameter

Question

I have two unit tests as follows:

    [DataTestMethod]
    [DataRow(1, 1, 2)]
    [DataRow(2, 2, 4)]
    [DataRow(3, 3, 6)]
    public void AddTest1(int x, int y, int expected)
    {
        Assert.AreEqual(expected, x + y);
    }


    [DataTestMethod]
    [DataRow(new int[] { 1, 2, 3, 4 }, new int[] { 1, 3, 6, 10 })]
    [DataRow(new int[] { 1, 1, 1, 1, 1 }, new int[] { 1, 2, 3, 4, 5 })]
    [DataRow(new int[] { 3, 1, 2, 10, 1 }, new int[] { 3, 4, 6, 16, 17 })]
    public void AddTest2(int[] input, int[] expectedOutput)
    {
        Assert.AreEqual(input[0], expectedOutput[0]);
    }

The first unit test runs 3 times, once for each data row. The second unit test only runs once for the first DataRow.

How can I run the second UnitTests with the arrays once for each DataRow as well?

Can you please specify the test framework you are using? Also, can you fix the image so that it gets displayed in the question? — Julian
– Julian, Commented Oct 5, 2022 at 16:54

Julian · Accepted Answer · 2022-10-05 17:15:33Z

Most test frameworks require the test cases to use compile-time constants as parameters.

This works because the parameters are constant at compile time:

[DataTestMethod]
[DataRow(1, 1, 2)]
[DataRow(2, 2, 4)]
[DataRow(3, 3, 6)]
public void AddTest1(int x, int y, int expected)
{
    Assert.AreEqual(expected, x + y);
}

This doesn't work because you're not using compile-time constants:

[DataTestMethod]
[DataRow(new int[] { 1, 2, 3, 4 }, new int[] { 1, 3, 6, 10 })]
[DataRow(new int[] { 1, 1, 1, 1, 1 }, new int[] { 1, 2, 3, 4, 5 })]
[DataRow(new int[] { 3, 1, 2, 10, 1 }, new int[] { 3, 4, 6, 16, 17 })]
public void AddTest2(int[] input, int[] expectedOutput)
{
    Assert.AreEqual(input[0], expectedOutput[0]);
}

The new keyword with an array doesn't allow the test framework to differentiate (looking at the image you linked, it just says System.Int32[]).

A workaround might be this:

[DataTestMethod]
[DataRow(0, new int[] { 1, 2, 3, 4 }, new int[] { 1, 3, 6, 10 })]
[DataRow(1, new int[] { 1, 1, 1, 1, 1 }, new int[] { 1, 2, 3, 4, 5 })]
[DataRow(2, new int[] { 3, 1, 2, 10, 1 }, new int[] { 3, 4, 6, 16, 17 })]
public void AddTest2(int run, int[] input, int[] expectedOutput)
{
    Assert.AreEqual(input[0], expectedOutput[0]);
}

That way, the different test cases can be differentiated by a compile-time constant.

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