public void IsPlanetTestNull()
        {
            bool expected = false;
            bool actual;

            actual = GroupExtensions.IsPlanet(null);
            Assert.AreEqual(expected, actual);
        }
        public void IsPlanetTestSky()
        {
            Group sky = new Group("sky", GroupType.ReferenceFrame, null);

            bool expected = false;
            bool actual;

            actual = GroupExtensions.IsPlanet(sky);
            Assert.AreEqual(expected, actual);
        }
        public void IsPlanetTestEarth()
        {
            Group sun   = new Group("Sun", GroupType.ReferenceFrame, null);
            Group earth = new Group("Earth", GroupType.ReferenceFrame, sun);

            bool expected = true;
            bool actual;

            actual = GroupExtensions.IsPlanet(earth);
            Assert.AreEqual(expected, actual);
        }