Data driven test with "non-formattable" values are considered differently than those with "formattable" values

[drieseng]

Describe the bug

Data driven tests for which at least one of the value is "non-formattable" are handled differently than those where all values are "formattable".
When a data driven tests only has "formattable" values, each "row" is considered as a separate test.
When not all values are "formattable", the test method is considered as a single test with multiple results.

Steps To Reproduce

Compile and run the following test class:

using System.Globalization;

[TestClass]
public sealed class DataDrivenTests
{
    [DataTestMethod]
    [DynamicData(nameof(ConvertTo_Formattable_Data), DynamicDataSourceType.Method)]
    public void ConvertTo_Formattable(object value)
    {
    }

    [DataTestMethod]
    [DynamicData(nameof(ConvertTo_NonFormattable_Data), DynamicDataSourceType.Method)]
    public void ConvertTo_NonFormattable(object value)
    {
    }

    [DataTestMethod]
    [DynamicData(nameof(ConvertTo_FormattableAndNonFormattable_Data), DynamicDataSourceType.Method)]
    public void ConvertTo_FormattableAndNonFormattable(object value)
    {
    }

    private static IEnumerable<object[]> ConvertTo_Formattable_Data()
    {
        yield return new object[] { "UTF8" };
        yield return new object[] { "UTF32" };
    }

    private static IEnumerable<object[]> ConvertTo_NonFormattable_Data()
    {
        yield return new object[] { CultureInfo.InvariantCulture };
        yield return new object[] { CultureInfo.InvariantCulture };
    }

    private static IEnumerable<object[]> ConvertTo_FormattableAndNonFormattable_Data()
    {
        yield return new object[] { "UTF8" };
        yield return new object[] { "UTF32" };
        yield return new object[] { CultureInfo.InvariantCulture };
    }
}

Expected behavior

All three data driven test methods should be considered as multiple tests, one per "row" of test input.
This is how the ReSharper test runner reports the tests:

Actual behavior

Only the ConvertTo_Formattable test method is considered to be a "real" data driven test method with multiple inputs:

[Evangelink]

Thanks for the report, this is yet another example of why the current serialization mechanism is a wrong design... I'll close as duplicate of #1462