The type of an Array isn't inferred from properly

Using arrays of any dimension does not work in this example and ends up in the TestFixture failing to Set-up: (System.IndexOutOfRangeException trace)

static object[] populateTestCases = new object[]
        {
            new object[] { new int[40], 10}
        };

        [Test, TestCaseSource(nameof(populateTestCases))]
        public void PopulateTest<T>(T[] array, T value)
        {
            foreach (var item in array)
                Assert.AreEqual(item, value);
        }

However using a List<T> works fine: (The test compiles and behaves properly)

static object[] populateTestCases = new object[]
        {
            new object[] { new List<int>(40), 10}
        };

        [Test, TestCaseSource(nameof(populateTestCases))]
        public void PopulateTest<T>(List<T> array, T value)
        {
            foreach (var item in array)
                Assert.AreEqual(item, value);
        }

[CharliePoole]

Looks like a bug (if confirmed) in the logic whereby NUnit deduces what type to use for a generic test method. It would probably give us some useful info if you tried reversing the order of the arguments.

Reversing the order doesn't help. (trace (don't think anything's changed))

static object[] populateTestCases = new object[]
        {
            new object[] { 10, new int[40]}
        };

        [Test, TestCaseSource(nameof(populateTestCases))]
        public void PopulateTest<T>(T value, T[] array)
        {
            foreach (var item in array)
                Assert.AreEqual(item, value);
        }

[CharliePoole]

Ah well, it was a thought and the result gives us more information.

[mikkelbu]

I just debugged the problem. When we enter GenericMethodHelper.TryGetTypeArguments we have that argList contain two elements: an int 10 and an integer array consisting of 40 zeroes. When we call TryApplyArgType for the array then we call with parmType is an T[] and argType is an Int32[].

But the code below fails as parmType.GetTypeInfo().ContainsGenericParameters returns true, but parmType.GetGenericArguments() returns an empty array, so for arrays we should probably use parmType.GetElementType() to get T.

nunit/src/NUnitFramework/framework/Internal/GenericMethodHelper.cs

Lines 110 to 117 in 1a34eac

	else if (parmType.GetTypeInfo().ContainsGenericParameters)
	{
	var genericArgTypes = parmType.GetGenericArguments();
	if (argType.HasElementType)
	{
	ApplyArgType(genericArgTypes[0], argType.GetElementType());
	}