launchpad-dev team mailing list archive

[Jonathan Lange <jml@xxxxxxxxxxxxx>]

On Tue, May 4, 2010 at 2:33 PM, Aaron Bentley <aaron@xxxxxxxxxxxxx> wrote:
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> On 05/03/2010 09:47 PM, Tim Penhey wrote:
>> This uses a Fixture that jml wrote a while ago for the scanner (which has
>> since been removed).  The fixture code was moved to lp.testing.fixture.  If you
>> have a need to use something in your tests that has a setUp and tearDown, you
>> can define a fixture, and use the TestCase method installFixture.
>
> This sounds a lot like a Context Manager.  Should they be unified?  If
> not, how should we choose which to use?
>

They serve a similar purpose, to be sure.

Please forgive me, but the best way I can answer right now is to think
out loud and not come to a conclusion. I hope it helps.

A bunch of things have setUp and tearDown methods, things like bzr
Server objects. Some of these things are relatively complicated and
benefit from having an addCleanup method. Hence, the Fixture base
class. I'm going to call anything with a setUp and tearDown method a
fixture for the rest of this email.

Since these fixtures are frequently used in tests, it's nice to have a
convenient way of saying "run this test with this fixture". Especially
since "fixture.setUp(); self.addCleanup(fixture.tearDown)" is
boilerplate. self.installFixture(FooFixture()) seems as good a way as
any, especially in Python 2.4 land.

In Python 2.5 land, we have Context Managers. I guess any test that
uses addCleanup now (never mind Fixture) could be rewritten to use a
context manager instead. I'm genuinely uncertain as to whether that
would be an improvement, but guess not.

It would certainly be nice to have something like installFixture that
takes a Context Manager instead of a thing that has setUp and
tearDown. It would probably be nice to have a thing that adapts
objects with setUp/tearDown and turns them into Context Managers,
since it would eliminate the need for two methods that do basically
the same thing, and since it would let us use things like bzr Servers
with the 'with' notation.

Maybe Launchpad classes that have setUp and tearDown (like Fixture)
should be changed to be context managers. I genuinely don't know
whether that would be an improvement. I don't really know how many we
have (excluding tests). I also don't know how many context managers we
have.

jml