Akos,
that is exactly the kind of problem I'm talking about! Right down to the
detail about stopping work and returning to the project later, and seeing
all the tests pass!
--
Jonathon McKitrick
On Tue, Jan 6, 2015 at 3:22 AM, Akos Gyimesi <a...@gyim.hu> wrote:
>
> On Sat, Jan 3, 2015, at 02:46 AM, Brian Marick wrote:
> >
> > > I use TDD and mocking/stubbing (conjure) to test each layer of my code.
> > > The problem is when I change the function signature and the tests do
> not
> > > break, because the mocks/stubs do not know when their argument lists no
> > > longer agree with the underlying function they are mocking. Is there a
> > > way to catch this? Short of a test suite that eschews stubbing in
> favor
> > > of full setup/teardown of DB data for each test?
> >
> > Could you give an example? I use mocks fairly heavily, and I don't seem
> > to have this problem. Perhaps it's because I change the tests before the
> > code?
>
> Although the subject changed a little bit, I would be still interested
> in your approach to refactoring if there is heavy use of mocking. Let me
> give you an example:
>
> Let's say I am writing a login form, trying to use the top-down approach
> you described. My approach could be the following:
>
> (unfinished check-pw)
>
> (fact "login-form succeeds if user enters the correct password"
> (login-form-success? {:username "admin" :password "secret"}) => true
> (provided
> (db/get-user "admin") => (contains (:password "my-secret-hash"))
> (check-pw "my-secret-hash" "secret") => true))
>
> (defn login-form-success? [user-input]
> (let [user (db/get-user (:username user-input))]
> (check-pw (:password user) (:password user-input))))
>
> Then I finish the check-pw function and everything works.
>
> Now, later that day I decide that I pass the whole user object to the
> check-pw function. Maybe I want to use the user ID as a salt, or maybe I
> just want to leave the possibility for checking password expiration,
> etc. So I modify the test and the implementation of check-pw so that the
> first parameter is the user object, not the password hash.
>
> Suddenly my co-worker comes to me saying "hey, I need you on a meeting
> right now!" I close my laptop, and an hour later I think "where were
> we?..." I run all the tests, and they all pass, so I commit.
>
> Except... I forgot to modify all the invocations of check-pw in both the
> test and the implementation. Every test pass, so I have no way of
> finding out the problem without careful code review or by examining the
> stack traces from the live code.
>
> While this bug is easy to catch, what if my function is mocked in
> several places, and I fail to rewrite all of them properly?
>
> Do you have any advice on what you would have done differently here to
> avoid this bug?
>
> Regards,
> Akos
>
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