Assert method for strings

[josef-poetzl]

vbNullstring (VBA: StrPtr = 0) is null in C#.
Add a Assert methode to compare strings (with string parameters for actual/expected)

Possible variants (interface for VBA):

• Assert.AreEqual Expected, Actual, "InfoText", ++ string compare parameter ++
• Assert.StringCompare(IgnoreCase:=False, VbNullStringEqualEmptyString:=True).AreEqual Expected, Actual
• Assert.StringCompare(Compare:= vbTextCompare).AreEqual Expected, Actual
• Assert.StringCompare(....).That Actual, Iz.EqualTo(Expected)

Note: Maybe this is useful for other data types as well.