Migration: Handle NUnit ExpectedResult attribute property

[thomhurst]

Summary

The NUnit to TUnit migration code fixer should handle the ExpectedResult property in NUnit test attributes and convert it to TUnit's assertion style.

NUnit Pattern

[TestCase(2, 3, ExpectedResult = 5)]
public int Add(int a, int b)
{
    return a + b;
}

[TestCase("hello", ExpectedResult = 5)]
public int GetLength(string input)
{
    return input.Length;
}

Expected TUnit Output

[Test]
[Arguments(2, 3)]
public async Task Add(int a, int b)
{
    await Assert.That(a + b).IsEqualTo(5);
}

[Test]
[Arguments("hello")]
public async Task GetLength(string input)
{
    await Assert.That(input.Length).IsEqualTo(5);
}

Implementation Notes

1. Detect ExpectedResult = <value> in NUnit attributes ([TestCase], [TestCaseSource], etc.)
2. Remove ExpectedResult from the migrated [Arguments] attribute
3. Change method return type from T to async Task
4. Wrap the return expression with await Assert.That(<expr>).IsEqualTo(<expected>)
5. Handle various return types (int, string, bool, objects, etc.)

Edge Cases to Consider

• Methods with multiple return statements
• Methods with complex return expressions
• Generic return types
• Nullable return types
• ExpectedResult = null