The StringAssert class is contained in the nunit.framework.extensions assembly and provides a number of methods that are useful when asserting on string values.
StringAssert.Contains( string expected, string actual );
StringAssert.Contains( string expected, string actual,
string message, params object[] args );
StringAssert.ContainsAny( string expected, string actual );
StringAssert.ContainsAny( string expected, string actual,
string message, params object[] args );
StringAssert.StartsWith( string expected, string actual );
StringAssert.StartsWith( string expected, string actual,
string message, params object[] args );
StringAssert.EndsWith( string expected, string actual );
StringAssert.EndsWith( string expected, string actual,
string message, params object[] args );
StringAssert.AreEqualIgnoringCase( string expected, string actual );
StringAssert.AreEqualIgnoringCase( string expected, string actual,
string message params object[] args );