assertNumQueries is buggy with views and the test client if used more than once in a test

[Luke Plant]

With code like this:

with self.assertNumQueries(5):
    self.client.get("some/view/")

with self.assertNumQueries(5):
    self.client.get("some/view/")

The second one always fails, with '0' being the number of queries it calculates. (I do not have any caching enabled).

If the second client.get goes to a view that actually uses less queries than the first, then assertNumQueries calculates a negative number of queries, which seems to be the true number minus the number of queries from the last assertNumQueries. I can't quite pin down the behaviour.

I'm guessing this has to do with the way test client/request life-cycle/connections interact. I do not see this with normal queries done directly in the function.

If someone else could confirm that would be helpful.

This happens:

• Using assertNumQueries either with the 'with' statement or passing a function in.
• with SQLite (haven't tested with others)
• with or without the TransactionMiddleware

[Alex Gaynor]

Almost certainly caused by the reset_queries signal: ​http://code.djangoproject.com/browser/django/trunk/django/db/__init__.py#L87 . I'll think on what can be done about this, as for obvious reasons the context manager/function records the number of queries before it calls the function, and then clears it. Perhaps this function should respect use_debug_cursor or something. Again, needs thoughts.

[Jonas Obrist]

tests for 14774 (they're failing at the moment)

[Jonas Obrist]

I've added some tests but they fail with -3!=1. How would assertNumQueries think that there's negative queries? Is this an issue with my tests or an actual issue with assertNumQueries?

[Luke Plant]

Replying to ojii:

Is this an issue with my tests or an actual issue with assertNumQueries?

It's an issue with assertNumQueries - I also saw assertNumQueries thinking that a negative number of queries had occurred. The only workaround at present is to use the view functions directly, rather than using the client interface.

[Jonas Obrist]

fixed this issue by wrapping the reset_queries signal in the assertNumQueries context

[Alex Gaynor]

(In [15251]) Fixed #14774 -- the test client and assertNumQueries didn't work well together. Thanks to Jonas Obrist for the initial patch.

[Jacob]

Milestone 1.3 deleted