public void RemoveNumbersMutatorTest(string input, string expectedResult)
        {
            IStringMutator stringMutator = new RemoveNumbersMutator();

            string actual = stringMutator.Mutate(input);

            Assert.Equal(expectedResult, actual);
        }
        public void NullHandlingTest()
        {
            IStringMutator stringMutator = new ToUpperMutator();
            var            result        = stringMutator.Mutate(null);

            Assert.Null(result);

            stringMutator = new InvertMutator();
            result        = stringMutator.Mutate(null);
            Assert.Null(result);

            stringMutator = new RemoveNumbersMutator();
            result        = stringMutator.Mutate(null);
            Assert.Null(result);

            stringMutator = new TrimMutator();
            result        = stringMutator.Mutate(null);
            Assert.Null(result);
        }