Is there a way to test combining both TestServer and moq Mock to replace methods in classes in ConfigureTestServices?

Question

I am able to do integration tests using TestServer, and I can manually mock methods in any DI injected class by replacing in ConfigureTestServices the class by a mocking one as follows :

var webHostBuilder =
    new WebHostBuilder()
        .UseEnvironment("Testing")
        .UseContentRoot(projectDir)
        .ConfigureTestServices(s =>
        {
            s.TryAddTransient(IMyClass, MyMockMyClass);
        })
        .UseStartup<Startup>();

Where MyMockMyClass is a remplacement of MyClass, with the purpose of replacing a method (eg: Method1).

Is there an option to use a moq Mock.Of<MyClass> to quickly replace on the fly my Method1, without the need to create a new class MyMockMyClass? Something like :

var mymock = Mock.Of<IMyClass>();
Mock.Get(mymock ).Setup(m => m.Method1(It.IsAny<string>()).Returns(value: whatever);

And then somehow using this mymock with the line s.TryAddTransient(IMyClass, ... in the ConfigureTestServices code above?

Answer 1

Have the factory delegate return the mocked services when configuring the test server

var mymock = Mock.Of<IMyClass>();
Mock.Get(mymock)
    .Setup(m => m.Method1(It.IsAny<string>())
    .Returns(value: whatever);

var webHostBuilder =
    new WebHostBuilder()
        .UseEnvironment("Testing")
        .UseContentRoot(projectDir)
        .ConfigureTestServices(services => {
            services.RemoveAll<IMyClass>();//Remove previous registration(s) of this service
            services.TryAddTransient<IMyClass>(sp => mymock);
        })
        .UseStartup<Startup>();

If you need a new mocked instance per call then move the logic into the factory delegate