Returns delegate function NSubstitute

Question

I am trying to test a delegate function using NSubstitute:

_myMock.CallDelegateIfKeyMissing(Arg.Any<string>, Arg.Any<Func<Task<string>>>())
.Returns(
   //The results of the delegate function "Arg.Any<Func<Task<string>>>"
);

Is this possible please? Thank you

Answer 1

You can access the Func<Task<string>> argument from within the Returns and invoke it:

_myMock
    .CallDelegateIfKeyMissing(Arg.Any<string>(), Arg.Any<Func<Task<string>>>())
    .Returns(
        x => x.Arg<Func<Task<string>>>().Invoke()
    );

var result = _myMock.CallDelegateIfKeyMissing("hi", () => Task.FromResult("world"));

Assert.Equal("world", result.Result);

There's a bit more information in the NSubstitute documentation.