Output Parameters in Argument Contraints with Rhino Mocks

Today, I was writing tests for a method that had an output parameter in its argument list. With Rhino Mocks, this can be very simple and straightforward. In the cookie-cutter example, you can simply pass in the output parameter the same way you’d pass it to the function.

bool outParam;
var mock = MockRepository.GenerateMock<ISomeInterface>();
mock.Expect(x => x.MethodWithAnOutParam(out outParam));

But, what if you want to use argument constraints? It becomes a little less obvious but still very easy.

var mock = MockRepository.GenerateMock<ISomeInterface>();
bool refParam;
mock.Expect(x => x.MethodWithARefParam(
    Arg<string>.Is.Anything, 
    ref Arg<bool>.Ref(Is.Anything(), true).Dummy));

Note that the value in parentheses is the value that will be assigned to the output parameter passed into the function.

You can use the Ref constraint to similarly deal with ref parameters. Notice that the Ref constraint takes two arguments, though: a Rhino AbstractConstraint and the return value.

var mock = MockRepository.GenerateMock<ISomeInterface>();
bool outParam;
mock.Expect(x => x.MethodWithARefParam(
    Arg<string>.Is.Anything, 
    ref Arg<bool>.Ref(Is.Anything(), true).Dummy));
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