Improve Testability

[jaredcnance]

A primary goal of this task is to make it easy to write end to end tests without thinking about json:api.

• Decouple deserialization (depends on Posting JSONAPI data not binding #237)
• Fluent testing API (RFC: Fluent Testing API #294)
• Possible issue with data type precision during deserialization (needs investigation)
• Documentation around best practices for testing
• Improve exception messages during serialization
• Need to include comment (or come up with better solution) about how to use IScopedServiceProvider. See ScopedServiceProvider should throw helpful exception when outside HttpContext #362 for interim solution.
• Should provide a simple way to create the ResourceGraph and JsonApiContext outside of a web request.
  Current workaround:

    public class MockJsonApiContextFactory
    {
        public static Mock<IJsonApiContext> GetWithSingleResource<TResource, TId>() 
            where TResource : class, IIdentifiable<TId>
        {
            var resourceGraph = new ResourceGraphBuilder()
                .AddResource<TResource, TId>()
                .Build();

            var requestEntity = resourceGraph.GetContextEntity(typeof(TResource));
            var jsonApiContextMock = new Mock<IJsonApiContext>();
            jsonApiContextMock.Setup(c => c.ResourceGraph).Returns(resourceGraph);
            jsonApiContextMock.Setup(c => c.RequestEntity).Returns(requestEntity);
            return jsonApiContextMock;
        }
    }

• Consider adding "enhanced exception messages" if the environment is test (or something along those lines)

https://github.com/json-api-dotnet/JsonApiDotNetCore/blob/master/test/UnitTests/TestScopedServiceProvider.cs

[maurei]

JsonApiContext does no longer exist. #558. This greatly improves testability.