public void TeachingAssistantCanTeachTwoClasses()
        {
            var underTest = new TeachingAssistant(3);
            underTest.AddClassTitle("Biology 101");
            underTest.AddClassTitle("Physics 206");


            Assert.Equal("Biology 101", underTest.ClassTitles.First());
            Assert.Equal("Physics 206", underTest.ClassTitles.Last());
            Assert.Equal(2, underTest.ClassTitles.Count());
        }
        public void TeachingAssistantCanTeachNoMoreThanTwoClasses()
        {
            var underTest = new TeachingAssistant(3);
            underTest.AddClassTitle("Biology 101");
            underTest.AddClassTitle("Physics 206");
            Assert.Throws<InvalidOperationException>(() => underTest.AddClassTitle("Chemistry 112"));


            Assert.Equal("Biology 101", underTest.ClassTitles.First());
            Assert.Equal("Physics 206", underTest.ClassTitles.Last());
            Assert.Equal(2, underTest.ClassTitles.Count());

        }
        public void TeachingAssistantCanReplaceAClass()
        {
            var underTest = new TeachingAssistant(3);
            underTest.AddClassTitle("Biology 101");
            underTest.AddClassTitle("Physics 206");
            underTest.RemoveClassTitle("Biology 101");
            underTest.AddClassTitle("Chemistry 112");


            Assert.Equal("Chemistry 112", underTest.ClassTitles.First());
            Assert.Equal("Physics 206", underTest.ClassTitles.Last());
            Assert.Equal(2, underTest.ClassTitles.Count());

        }
        public void TeachingAssistantCanTeachASingleClass()
        {
            var underTest = new TeachingAssistant(3);
            underTest.AddClassTitle("Biology 101");

            Assert.Equal("Biology 101", underTest.ClassTitles.Single());
        }