Re: testing macros and fixtures

[Artur Malabarba <bruce.connor.am@gmail.com>]

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2015-10-12 22:13 GMT+01:00 Phillip Lord

> ERT is quite nice, but one of the things that I have found lacking is a
> nice set of predicates, for use within should.
>
> So, when I wrote test for my "lentic" package I needed some functions
> like, so that I could do things like:
>
> (should
>   (test-eq-after-this
>      "blah-before.txt"
>      "blah-after.txt"
>      (insert "hello")))
>
> which opens "blah-before.txt" runs (insert "hello") then compares the
> result with "blah-after.txt".

I think that's a pretty specific use-case. So it's best to let people write
their own macros for this.

(defmacro should-eq-after-body (file-before file-after &rest body)
  `(let ((bef
          (with-temp-buffer
            (insert-file-contents file-before)
            ,@body
            (buffer-string))))
     (should (string= bef (with-temp-buffer
                            (insert-file-contents file-after)
                            (buffer-string))))))

> My version of this also does a diff of the
> results if the two are not equal.

This certainly seems very useful. Maybe ert should do this on *all*
multi-line string comparisons instead of doing its default
“different-strings” report (which, most of the time, just says “strings are
of different length”).

> I've noticed that "puppet-mode" has some thing similar. For instance:
> ...
>
> And julia-mode has indentation checking tests like so:
>
> ...
>
> My own experience is that these are actually quite hard to right. The
> ones in lentic have never worked quite right -- that is, when it all
> works they are fine, but restoring state after a crash doesn't always
> work. Similarly, checking that, for example, test files are not already
> open before a test is run interactively.

Yes, there are many packages that use custom-deisgned temp-buffers for
testing. In fact, most non-trivial packages do. I'd really like to see ert
offer a common interface for this. The difficulty for that is that each
package has very different needs when it comes to testing in buffers, so I
have no idea what this common interface could be.

> So, the point of my question is this; are there any good libraries
> providing this kind of fixture logic?

Don't know.

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