public void InverseOfReadOnly() { var readOnly = new ReadOnlyDictionary <int, string>(ValidDictionary); var readOnlyInverse = readOnly.Inverse(); Assert.That(readOnlyInverse, Is.TypeOf <ReadOnlyDictionary <string, int> >()); Assert.That(readOnlyInverse, Is.Not.TypeOf <Dictionary <string, int> >()); }