public async Task DeleteGroupAsync_WrongIdShouldReturnStatusBadRequest(int id)
        {
            //Arrange
            var groupServiceMock = Substitute.For <IGroupService>();
            var sut = new GroupsController(groupServiceMock);

            //Act
            var response = await sut.DeleteGroupAsync(id);

            //Assert
            Assert.Equal(400, ((StatusCodeResult)response).StatusCode);
        }
        public async Task DeleteGroupAsync_NotExistingIdShouldReturnStatusNotFound()
        {
            //Arrange
            var groupServiceMock = Substitute.For <IGroupService>();
            var sut = new GroupsController(groupServiceMock);

            //Act
            var response = await sut.DeleteGroupAsync(100500);

            //Assert
            await groupServiceMock.Received().DeleteByIdAsync(100500);

            //Assert.Equal(404, ((StatusCodeResult) response).StatusCode);
        }
        public async Task DeleteGroupAsync_ShouldReturnStatusOk()
        {
            //Arrange
            var groupServiceMock = Substitute.For <IGroupService>();
            var groupToRemove    = new Group {
                Id = 1, Name = "someName", Country = "someCountry", CreationYear = 2000
            };
            var sut = new GroupsController(groupServiceMock);

            //Act
            var response = await sut.DeleteGroupAsync(1);

            //Assert
            await groupServiceMock.Received().DeleteByIdAsync(1);

            //Assert.Equal(200, ((StatusCodeResult) response).StatusCode);
        }