学习F＃：是否可以创建一个测试用例来验证签名？

Question

With unit-testing several hundred lines of F# code I realized that it would be advantageous to not only check the output but also the signatures. The reason being if the code is validated for a release and then changes are made after the release that modify the signature, one would want to know why the signature changed so that either the test case can be updated for the new signature or to flag the change as causing a problem.

Is it possible to create a test case to verify a signature? If so, how?

Answer 1

I think the best approach would be to simply provide test cases which cover the bounds of your signature. eg, to verify that a return type is an int ,

let x:int = someFunc() //you'll get a compiler error if the return type changes

Really, I'd expect that just by virtue of exhaustively testing your public API, you will have necessarily tested the signatures. Especially in a language like F#, which has a relatively strict static type system.

I suppose you could also venture to use reflection to assert signatures, but honestly I don't think that would be such a good investment of time.

Answer 2

As said by Stephen, if you write some unit tests for your code, the unit tests will generally call the function with values of the type that the function require, so that will automatically also check the signature (if you change the signature, you will not be able to compile your tests).

Another alternative, which is suitable for libraries is to use F# interface files ( .fsi ). The interface file specifies types of public functions in the implementation file ( .fs ) and it is also a good place for documentation.

If you then (accidentally) change the type of your implementation, your code will not compile unless you update the type in the interface file.

You will probably want to maintain the interface file by hand (see F# library sources for a good example), but you can get an initial by calling the compiler with --sig:mylibrary.fsi . You could probaby use this switch to automate the testing (and check the diff between signature files after each compilation).