String not-regex constraint succeeds non-string actual value

[RenderMichael]

The following code passes

[Test]
public void StringMatchesRegex()
{
    // lang=regex
    string regex = "[0-9]";
    string? actual = null;
    Assert.That(actual, Does.Not.Match(regex));
}

Should the RegexConstraint throw an ArgumentException for non-string values (like null)?

If so, that a 2-line change (plus tests) and I can spin up the PR myself.

[OsirisTerje]

Well,.... null does not match any regex, so the statement there is true.

You could try:

Assert.That(actual, Is.Not.Null.And.Does.Not.Match(regex));

[RenderMichael]

null does not match any regex

That's a philosophical statement, and I see the point.

On the other hand, .NET's built-in regex throws when calling Matches(null).

Additionally, the constraint calls actual is string actualStr && Regex.Matches(actualStr) (pseudocode since I don't have the code in front of me).

So the following also passes, although it's flagged by NUnit.Analyzers

[Test]
public void StringMatchesRegex()
{
    // lang=regex
    string regex = "[0-9]";
    int actual = 1;
    Assert.That(actual, Does.Not.Match(regex));
}

edit: in fact, that's good broadening of the issue, I'll rename it

[OsirisTerje]

On the other hand, .NET's built-in regex throws when calling Matches(null)

If .Net does so, we should probably do the same.

[RenderMichael]

Would love to be assigned this PBI, I can spin up a PR for it

[OsirisTerje]

There you are :-) Have fun!