public void ProveThatPolymorphismIsApparent()
        {
            Tiger  tiger = new Tiger();
            Frog   frog  = new Frog();
            Animal bird  = new Bird();

            string expectedTiger = "food";
            string expectedFrog  = "Bugs";
            string expectedBird  = "Dirt and stuff";

            Assert.Equal(expectedTiger, tiger.Diet());
            Assert.Equal(expectedFrog, frog.Diet());
            Assert.Equal(expectedBird, bird.Diet());
        }