System.Text.RegularExpressions test fails on Browser wasm

[mdh1418]

CharactersComparedOneByOne_Invariant in RegexCultureTests.cs fails when running library tests on Browser with

Assert.StartsWith() Failure:
Expected: Ö‍
Actual:   Ö

Tagging subscribers to this area: @eerhardt, @pgovind
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[safern]

I think this is the expected behavior on GlobalizationMode.Invariant and that test run was done in invariant mode. If I run these tests on any runtime on Invariant mode I get the same result. See: #39470 (comment)

cc: @tarekgh

[tarekgh]

I am a little bit confused here. the description of the issue is showing the expected result matching the actual result. so why this is failing?

[safern]

because the unicode points are different but the console is showing it correctly cause it understands unicode.

[tarekgh]

but the console is showing it correctly cause it understands unicode.

Usually this happen visually and not really changing the underlying Unicode codepoints. so I expect still to be 2 different strings even if they are showing same. but this is not the case here as the underlying strings are exactly same. do you have a pointer to the test case?

[safern]

This is the line that is failing:

runtime/src/libraries/System.Text.RegularExpressions/tests/RegexCultureTests.cs

Line 48 in 6072e4d

Assert.StartsWith(S1, S2, StringComparison.InvariantCulture);

The two unicode points are: \u00D6\u200D and \u004F\u0308 which both are O umlaut together, but char by char they're different (So the underlying strings are different).

[tarekgh]

The part I don't understand is who converted \u004F\u0308 to \u00D6? to clarify more I would expect the text displayed as Ö which actually 2 codepoints \u004F\u0308 and not just \u00D6.

[safern]

I see, I believe the problem is in Xunit itself. The exception is constructed with the string itself:
https://github.com/xunit/assert.xunit/blob/3af483c3e851ef4f463a8ce8b9399b7bc8ab4dc0/StringAsserts.cs#L115

And then Xunit is setting the exception message with those strings which will be the full underlying strings:
https://github.com/xunit/assert.xunit/blob/3af483c3e851ef4f463a8ce8b9399b7bc8ab4dc0/Sdk/Exceptions/StartsWithException.cs#L31

And that's why the console shows them like that.

[safern]

Closing per discussion above.