How to check if directory 1 is a subdirectory of dir2 and vice versa

Question

What is an easy way to check if directory 1 is a subdirectory of directory 2 and vice versa?

I checked the Path and DirectoryInfo helperclasses but found no system-r

Answer 1

With help from the great test cases written in angularsen's answer, I wrote the following simpler extension method on .NET Core 3.1 for Windows:

public static bool IsSubPathOf(this string dirPath, string baseDirPath)
{
    dirPath = dirPath.Replace('/', '\\');
    if (!dirPath.EndsWith('\\'))
    {
        dirPath += '\\';
    }

    baseDirPath = baseDirPath.Replace('/', '\\');
    if (!baseDirPath.EndsWith('\\'))
    {
        baseDirPath += '\\';
    }

    var dirPathUri = new Uri(dirPath).LocalPath;
    var baseDirUri = new Uri(baseDirPath).LocalPath;

    return dirPathUri.Contains(baseDirUri, StringComparison.OrdinalIgnoreCase);
}