c# - Moq and validating a private method ios called with correct parameters

Question

I'm probably below average on Unit Testing skills, but been asked to write a unit test for something I fixed. Basically, a method now allows a null value to be passed in, and I need to validate that it gets switched to the correct value, if null.(Please note, method code reduced to remove supurfluous code - it actually does more than return true...)

 public IDictionary<string, JToken> MethodINeedToTest(
            long? userId,
            long? orgId
        )
 {
       userId ??= DataServicesHelper.SystemUserKey;
            
       var myResults = APrivateMethod(userId.Value, orgId, false);

       return true;
}

I was hoping to just verify that APrivateMethod was called with the value from DataServicesHelper.SystemUserKey. However, the method is private. So with Moq, I cannot do a verify on a private method (I believe).

Is there anyway to validate that when userId is passed in as null, the method is called with DataServicesHelper.SystemUserKey? (Other test is to validate that it gets called with userId when it's not null).

Or is the code just not testable?

question from:https://stackoverflow.com/questions/65910827/moq-and-validating-a-private-method-ios-called-with-correct-parameters

Answer 1

I think in this case there are 2 options.

1. Just let the APrivateMethod execute as is without any mocks and you validate the result that you get in both cases.
2. If option 1 is not possible due to the private method calling any outside service/repository then in that case you should try to use DI to inject those external dependencies that are used by the private method and then mock out those external calls.