[TIP] Fwd: [Launchpad-dev] Reminder about a great Testtools matcher

[Herman Sheremetyev]

On Wed, Jul 20, 2011 at 10:08 AM, Martin Pool <mbp at sourcefrog.net> wrote:
> I thought this was cool enough it might be of interest to t-i-p.
> Martin
>
>
>
> ---------- Forwarded message ----------
> From: Julian Edwards <julian.edwards at canonical.com>
> Date: 19 July 2011 22:11
> Subject: [Launchpad-dev] Reminder about a great Testtools matcher
> To: Launchpad Community Development Team <launchpad-dev at lists.launchpad.net>
>
>
> I hope you all have the documents for Testtools[1] matchers on speed dial
> because they are awesome.  I thought I'd remind you about the
> MatchesStructure
> matcher because I used it a while ago, forgot about it, and re-discovered it
> recently.
>
> Check out this diff snippet:
>
> -        self.assertEqual(source_name, copy_job.package_name)
> -        self.assertEqual(version, copy_job.package_version)
> -        self.assertEqual(target_archive, copy_job.target_archive)
> -        self.assertEqual(source_archive, copy_job.source_archive)
> -        self.assertEqual(to_series, copy_job.target_distroseries)
> -        self.assertEqual(to_pocket, copy_job.target_pocket)
> -        self.assertFalse(copy_job.include_binaries)
> -        self.assertEquals(PackageCopyPolicy.INSECURE, copy_job.copy_policy)
> +        self.assertThat(copy_job, MatchesStructure(
> +            package_name=Equals(source_name),
> +            package_version=Equals(version),
> +            target_archive=Equals(target_archive),
> +            source_archive=Equals(source_archive),
> +            target_distroseries=Equals(to_series),
> +            target_pocket=Equals(to_pocket),
> +            include_binaries=Equals(False),
> +            copy_policy=Equals(PackageCopyPolicy.INSECURE)))
>
> I replaced a load of serially-processed assertions with a single assertion.
> This is good because:
>
>  * It checks all of the conditions, not just up until the first one fails.
>  * It prints out all the values if any of them fail to match.
>
> I hope to see more use of this pattern!

I hope not. I would hope to see more smaller tests rather than armies
of asserts in a single test. Yes, it's necessary to have multiple
asserts per test at times, but in a case like the above where you're
comparing properties on the same object, the fact that you're doing
separate asserts should steer you toward writing a better equality
operator on that object rather than bunching a ton of asserts into a
single statement.

-Herman