public void StartsWithTest()
        {
            var mondaiWords0 = new []
            {
                new MondaiWord("This"),
                new MondaiWord("is"),
            };
            var mondaiWords1 = new []
            {
                new MondaiWord("this"),
                new MondaiWord("is"),
            };
            var mondaiWords2 = new []
            {
                new MondaiWord("aaa"),
                new MondaiWord("This"),
                new MondaiWord("is"),
            };
            var mondaiWords3 = new []
            {
                new MondaiWord("This is"),
                new MondaiWord("an apple."),
            };

            {
                var rightAnswer = new CorrectAnswer("This is an apple.");
                rightAnswer.CorrectAnswerHelper = new CorrectAnswerHelperUsingRegex(rightAnswer);

                {
                    var s = MondaiWord.SimplyJoin(mondaiWords0);
                    Assert.AreEqual("This is", s);
                    var p = "^" + MondaiWord.GetRegexPattern(s);
                    Assert.AreEqual(@"^This\s+is", p);
                    StringAssert.IsMatch(p, rightAnswer.Text);
                }

                Assert.Throws<ArgumentNullException>(() => { rightAnswer.StartsWith(null); });
                Assert.True(rightAnswer.StartsWith(new MondaiWord[0]));

                Assert.True(rightAnswer.StartsWith(mondaiWords0));
                Assert.False(rightAnswer.StartsWith(mondaiWords1));
                Assert.False(rightAnswer.StartsWith(mondaiWords2));
                Assert.True(rightAnswer.StartsWith(mondaiWords3));
            }
            {
                var rightAnswer = new CorrectAnswer("This is an apple.");
                rightAnswer.CorrectAnswerHelper = new CorrectAnswerHelperUsingNormalizer(rightAnswer);

                Assert.Throws<ArgumentNullException>(() => { rightAnswer.StartsWith(null); });
                Assert.True(rightAnswer.StartsWith(new MondaiWord[0]));

                Assert.True(rightAnswer.StartsWith(mondaiWords0));
                Assert.False(rightAnswer.StartsWith(mondaiWords1));
                Assert.False(rightAnswer.StartsWith(mondaiWords2));
                Assert.True(rightAnswer.StartsWith(mondaiWords3));
            }
        }