Tests should be aware of the Current Culture Info

Hello,

As i'm French, my CultureInfo.CurrentCulture is set to "fr-FR" while running tests.
But for some tests, especially for the ToString() methods, tests are write to check "en-US" Culture.
Could you keep one of these using en-us culture? I think there's some value in at least testing with one explicit culture here. As is, both of these calls will use CultureInfo.CurrentCulture (no-params ToString calls with CultureInfo.CurrentCulture). Same applies to the other tests on the other types.