The entire point of using JustMock is to create mock objects, i.e. objects that look just like the real objects, i.e. they implement the same interfaces, derive from the same base class, but the don't have an actual implementation. If you wanted to retain the actual implementation, you wouldn't need a mock - you would just use the actual type, instead.
I'm guessing here that you don't want to use the real implementation, but you still want to configure the mock object's behavior. To do that you need to arrange them. For example:
var mockContext = Mock.Create<Context>();
Mock.Arrange(() => contextFactory.Create()).Returns(mockContext);
In the above I arrange the return value of contextFactory.Create() to always be mockContext. I can then arrange the mockContext additionally to further configure its behavior as necessary for the test to succeed.
We have a great learning resource for JustMock and mocking in general located here
. I suggest that you peruse it to deepen your understanding of mocking and TDD in general. Your question should be answered in sufficient depth in "Day 12" of the series.
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