public async Task LogErrorIfNullMatReceivedFromObservable()
        {
            logger
            .Setup(
                l => l.Log(
                    LogLevel.Error,
                    It.IsAny <EventId>(),
                    It.Is <It.IsSubtype <IReadOnlyList <KeyValuePair <string, object> > > >((x, _) => x.ToString().Contains("null image received")),
                    It.Is <Exception>((e, _) => e == null),
                    It.IsAny <Func <It.IsSubtype <IReadOnlyList <KeyValuePair <string, object> > >, Exception, string> >()))
            .Verifiable("Logger was not called!");
            var observer = new RawImageObserver <Rgb>(logger.Object);

            var _ = Task.Run(async() =>
            {
                await Task.Delay(TimeSpan.FromMilliseconds(110));
                observer.OnNext(null);
            });

            try
            {
                await observer.GetImage();
            }
            catch (Exception)
            {
                // ignored - it's expected that GetImage will throw an exception, but this test checks that logger was called before that
            }

            logger.Verify();
        }
        public async Task ThrowInvalidOperationExceptionIfNullMatReceivedFromObservable()
        {
            var observer = new RawImageObserver <Rgb>(logger.Object);

            var _ = Task.Run(async() =>
            {
                await Task.Delay(TimeSpan.FromMilliseconds(110));
                observer.OnNext(null);
            });

            await Assert.ThrowsAsync <InvalidOperationException>(async() =>
            {
                await observer.GetImage();
            });
        }
        public async Task ReturnImageOnceItWasObserved()
        {
            var expectedFrame = new Mat(new Size(100, 100), DepthType.Cv32F, 3);
            Image <Rgb, byte> expectedImage = expectedFrame.ToImage <Rgb, byte>();
            var expectedJpeg = expectedImage.ToJpegData();

            var observer = new RawImageObserver <Rgb>(logger.Object);

            var _ = Task.Run(async() =>
            {
                await Task.Delay(TimeSpan.FromMilliseconds(110));
                observer.OnNext(expectedImage);
            });

            var image = await observer.GetImage();

            var actualJpeg = image.ToJpegData();

            Assert.Equal(expectedJpeg, actualJpeg);
        }