Tests with numeric strings fail under non-en-US culture

[amis92]

There is an issue with three tests in Avalonia.Markup.UnitTests.Data:

• Avalonia.Markup.UnitTests.Data.BindingExpressionTests.Should_Convert_Get_String_To_Double
• Avalonia.Markup.UnitTests.Data.BindingExpressionTests.Should_Convert_Set_Double_To_String
• Avalonia.Markup.UnitTests.Data.BindingExpressionTests.Should_Handle_DataValidation
• Avalonia.Visuals.UnitTests.Media.MatrixTests.Parse_Parses
• Avalonia.Visuals.UnitTests.Media.RectTests.Parse_Parses

When run under a culture that has another decimal separator than en-US full stop . (e.g. comma , in fr-FR), these tests fail as the conversion from/to string of these numeric values fails.

These tests surface a general problem: XAML type conversion is done with CurrentCulture which isn't explicitly set. I'm not exactly sure how it should behave, but I suspect that XAML parsing should be done explicitly in InvariantCulture (i.e. decimal separator is dot/full stop .).

[Gillibald]

My current PR already has the fix to this problem. We just have to use ToString(CultureInfo.CurrentCulture) for all values we compare to. I can create a separate PR for this to have it fixed faster.

Xaml conversion always justifies current culture and that's fine.

[amis92]

First off, for your changes it'd be much nicer to write $"{12.3}" (an approach used in xUnit tests) instead of ToString with culture.

Also, I think it'd be better off in it's own PR. These fixes are only valid for BindingExpressionTests, though.

With Rect and Matrix, it's not that simple, because they perform string.Split(new[]{',',' '}) which simply invalidates any culture-specific parsing later(edit: no longer, they use StringTokenizer). You'd have to either only use spaces as number separators, or use one depending on CurrentCulture, mirroring behavior of String Tokenizer.

They also differ in performing ToString: Rect uses InvariantCulture, Matrix CurrentCulture.

[Gillibald]

$"{12.3}" is just a shortcut to string.Format("{0}",12.3) which uses CurrentCulture by default. Don't know if that's allowed by code style conventions of this project.

Maybe you are right that numeric values should be parsed with invariant culture. That way everything should just work.

[Gillibald]

This can be closed

[amis92]

For the sake of reference, the Matrix/Rect cases were fixed by #1539