[FormRecognizer] Implement Model Factory for mocking support

[kinelski]

Fixes #11529.

[maririos]

One comment related to separate the ModelFactory for Training (and having it in the Training namespace)

[maririos]

FYI @lenniebriscoe

[lenniebriscoe]

FYI @lenniebriscoe

Many thanks for working on this. It will definitely improve testability. A few questions though.

1. I'm currently having to mock the FormRecognizerClient as below in order to work with the .StartRecognizeCustomFormsFromUriAsync() and .WaitForCompletionAsync(). Will there be a better way of doing this?

mockRecognizeCustomFormsOperation = new Mock<RecognizeCustomFormsOperation>("123/analyzeresults/123", mockFormRecognizerClient.Object);

 mockFormRecognizerClient
                .Setup(x => x.StartRecognizeCustomFormsFromUriAsync(It.IsAny<string>(),
                    It.IsAny<Uri>(), It.IsAny<RecognizeOptions>(),
                    It.IsAny<CancellationToken>()))
                .ReturnsAsync(mockRecognizeCustomFormsOperation.Object);

var responseBuilder = new ResponseBuilder().WithKeyValuePair("mapping_number", "10");

mockRecognizeCustomFormsOperation.Setup(x => x.WaitForCompletionAsync(It.IsAny<CancellationToken>()))
                .ReturnsAsync(responseBuilder.Build());

2. .WaitForCompletionAsync returns a Task<Azure.Response>. Currently, I have created a fake and am inheriting from Response. Again is there a better way of doing this?

[kinelski]

Hello, @lenniebriscoe.

Answering both of your questions: your approach is correct. That's how we designed mocking support in Azure SDK .NET libraries: service methods in clients/operations must be overridden, and model types can be instantiated by a static Model Factory. This is a guideline we follow in multiple libraries, so it's not likely to change soon.

Feel free to reach out if you have more questions!