public async Task Get_PlanetIsNull_ReturnNotFoundResult()
        {
            //Arrange
            var planetId      = 67;
            var planetService = Substitute.For <IPlanetsService>();
            var expected      = (Planet)null;

            planetService.GetPlanetOrDefaultAsync(Arg.Is(planetId)).Returns(Task.FromResult(expected));

            var sut = new PlanetsController(planetService);

            //Act
            var result = await sut.Get(planetId);

            //Assert
            Assert.IsType <NotFoundResult>(result);
        }
        public async Task Get_PlanetIsNotNull_ReturnOkObjectResultWithPlanet()
        {
            //Arrange
            var planetId      = 67;
            var planetService = Substitute.For <IPlanetsService>();
            var expected      = new Planet();

            planetService.GetPlanetOrDefaultAsync(Arg.Is(planetId)).Returns(Task.FromResult(expected));

            //Subject Under Test
            var sut = new PlanetsController(planetService);

            //Act
            var result = await sut.Get(planetId);

            //Assert
            var okObjectResult = result as OkObjectResult;

            Assert.Equal(expected, okObjectResult.Value);
        }