Unit tests fail on Linux for case-insensitive string comparisons

[axunonb]

While unit test succeed on Windows .NetFramework and Windows .NetCore, they fail on Linux .NetCore.

[axunonb]

The reason for this are the following methods in class SmartSettings:

internal IEqualityComparer<string> GetCaseSensitivityComparer()
{
    {
        switch (CaseSensitivity)
        {
            case CaseSensitivityType.CaseSensitive:
                return StringComparer.CurrentCulture;
            case CaseSensitivityType.CaseInsensitive:
                return StringComparer.CurrentCultureIgnoreCase;
            default:
                throw new InvalidOperationException(
                    $"The case sensitivity type [{CaseSensitivity}] is unknown.");
        }
    }
}

internal StringComparison GetCaseSensitivityComparison()
{
    {
        switch (CaseSensitivity)
        {
            case CaseSensitivityType.CaseSensitive:
                return StringComparison.CurrentCulture;
            case CaseSensitivityType.CaseInsensitive:
                return StringComparison.CurrentCultureIgnoreCase;
            default:
                throw new InvalidOperationException(
                    $"The case sensitivity type [{CaseSensitivity}] is unknown.");
        }
    }
}

The string are compared linguistically since many years. However, different platforms are handling this in different ways, and .NetCore makes use of the functions provided by the OS.

In most cases it can be assumed that selectors and variables should be comparable without language specifics. Examples why:

// Turkish character variations for "I"
CultureInfo.CurrentCulture = new CultureInfo("en-US");
string.Equals("i", "I", StringComparison.CurrentCultureIgnoreCase); // true
string.Equals("i", "İ", StringComparison.CurrentCultureIgnoreCase); // false

CultureInfo.CurrentCulture = new CultureInfo("tr-TR");
string.Equals("i", "I", StringComparison.CurrentCultureIgnoreCase)); // false
string.Equals("i", "İ", StringComparison.CurrentCultureIgnoreCase)); // true

// The Thai culture doesn't contain '.', so comparisons can be a surprising (tested on Ubuntu v18):
CultureInfo.CurrentCulture = new CultureInfo("th_TH.UTF8");
"Test".StartsWith(".", StringComparison.CurrentCulture); // true!!!
"12.4".IndexOf(".", StringComparison.CurrentCulture);    // 0

Conclusion: Internal comparisons should not be culture-specific, but Ordinal or OrdinalIgnoreCase respectively. However, this must be considered as a breaking change.