Assert(..., Is.EqualTo(...)) issues since 4.3.0

[moshekar]

After updating NUnit from 4.2.2 to 4.3.0, assertions of Is.EqualTo() are failing when the expected argument is not a string.
From what I see, the compiler selects the EqualTo(string? expected) overload.

For example, RedisValue is a struct, but the compiler still selects the string? version.
This causes Assert.That(redisResult, Is.EqualTo(RedisValue.Null) to fail even if redisResult == RedisValue.Null.

I could overcome this only by casting to object?: Assert.That(redisResult, Is.EqualTo((object?)RedisValue.Null)

Also I noticed headers (StringValues) comparisons now fail for assertions that succeeded before.

Using latest .net 9 with latest NUnit.

Thanks.

[OsirisTerje]

Thanks @moshekar !

Notifying @manfred-brands @stevenaw

[OsirisTerje]

I can reproduce the issue, added this: https://github.com/nunit/nunit.issues/tree/main/Issue4898

[moshekar]

Thanks @OsirisTerje
Here is another small project with both RedisValue and StringValues.
NUnitIssue4898.zip

if you downgrade NUnit to 4.2.2 all tests pass.
On 4.3.0 they fail.

[OsirisTerje]

I updated the repro with a test for a "normal" struct, and that works as it should.
Looking at code for the RedisValue, it is very complex struct, with overloads for nearly everything. We're obviously hitting on of those, but I am not sure what exactly that is being hit.

The RedisValue.Null is "just" a zero value, it is not a real null, so it should be working. But I guess we're fooled by the overloads there.

UPDATE: The RedisValue.Null is actually a null, contained in that property there.

[OsirisTerje]

Also I noticed headers (StringValues) comparisons now fail for assertions that succeeded before.

@moshekar Example please

[moshekar]

Also I noticed headers (StringValues) comparisons now fail for assertions that succeeded before.

@moshekar Example please

We've commented together, please see my last comment.

[OsirisTerje]

Thanks! I've added your code to the repro :-)

[OsirisTerje]

@manfred-brands @stevenaw

The StringValues test show what happens pretty well:

It breaks in the string comparison, due to the type cast there.

[moshekar]

Thanks @OsirisTerje
Please note that StringValues has implicit operator for string and also implements IEquatable<string?>
The operator doesn't work for casting with the as keyword.

[manfred-brands]

Thanks @moshekar, that gives me some ideas to fix this.

[OsirisTerje]

@moshekar @manfred-brands Yes, I noticed that. But it doesn't seems like we even get to any of the conversion in the StringValues class.

I added the code for the StringValues into the repro, just to check, and it doesn't hit anything there. So I believe the issue is the typecast we have in the generic ApplyTo method -