Do() should panic when given a function that returns values

[ash2k]

I've just spent an hour debugging a test where I by mistake used Do(func () string { ... return "some value" }) instead of DoAndReturn(). Do() just discarded the value and mock returned an empty string.

Do() should error out ASAP when given a function that returns values.

Thank you for the library!

[r-hang]

If I understand your issue correctly, this proposal turns a current no-op operation into a panic, which may break lots of existing tests that rely on this no-op behavior. One way to address this seems to be some type of linting to prevent this.

[ash2k]

Yes. There may also be tests that pass but don't actually test what the author thinks they are testing.

[tulzke]

Maybe it's worth excluding the return values from the function passed to Do? It's about the case when we pass the -typed flag to mockgen.
Example:

type SomeInterface{
    Action(value int) (bool, error)
}

func (MockSomeInterface) Do(func(value int)) {...}

func (MockSomeInterface) DoAndReturn(func(value int) (bool, error)) {...}