public async Task GetCustomGalleryItemAsync_WithImage_Equal()
        {
            var mockUrl      = "https://api.imgur.com/3/g/custom/AbcDef";
            var mockResponse = new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new StringContent(MockCustomGalleryEndpointResponses.GetCustomGalleryImage)
            };

            var client   = new ImgurClient("123", "1234", MockOAuth2Token);
            var endpoint = new CustomGalleryEndpoint(client,
                                                     new HttpClient(new MockHttpMessageHandler(mockUrl, mockResponse)));
            var galleryItem = await endpoint.GetCustomGalleryItemAsync("AbcDef").ConfigureAwait(false);

            Assert.NotNull(galleryItem);
            Assert.True(galleryItem is IGalleryImage);
        }
        public async Task GetCustomGalleryItemAsync_WithOAuth2TokenNull_ThrowsArgumentNullException()
        {
            var mockUrl      = "https://api.imgur.com/3/g/custom/AbcDef";
            var mockResponse = new HttpResponseMessage(HttpStatusCode.OK)
            {
                Content = new StringContent(MockCustomGalleryEndpointResponses.GetCustomGalleryImage)
            };

            var client   = new ImgurClient("123", "1234");
            var endpoint = new CustomGalleryEndpoint(client,
                                                     new HttpClient(new MockHttpMessageHandler(mockUrl, mockResponse)));

            var exception =
                await
                Record.ExceptionAsync(
                    async() => await endpoint.GetCustomGalleryItemAsync("AbcDef").ConfigureAwait(false))
                .ConfigureAwait(false);

            Assert.NotNull(exception);
            Assert.IsType <ArgumentNullException>(exception);
        }