#27539: assertNumQueries fails if debug cursor wrapper fills
---------------------------------------------+------------------------
Reporter: Malcolm Box | Owner: nobody
Type: Bug | Status: new
Component: Testing framework | Version: 1.10
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Recently I had a test fail that went like this:
{{{
with assertNumQueries(5):
response = self.client.get('/a/view')
# Various checks that the response had the correct data
}}}
This was failing with `AssertionError: 0 queries executed, 5 expected` yet
was hitting the database and returning the correct data. The failure only
happened when running certain subsets of the test suite - but not if run
in isolation.
Eventually I tracked this down to the following code in
`CaptureQueriesContext`
{{{
@property
def captured_queries(self):
return
self.connection.queries[self.initial_queries:self.final_queries]
def __enter__(self):
self.force_debug_cursor = self.connection.force_debug_cursor
self.connection.force_debug_cursor = True
self.initial_queries = len(self.connection.queries_log)
self.final_queries = None
request_started.disconnect(reset_queries)
return self
}}}
and this code in `BaseDatabaseWrapper`:
{{{
class BaseDatabaseWrapper(object):
queries_limit = 9000
def __init__(self, settings_dict, alias=DEFAULT_DB_ALIAS,
# Query logging in debug mode or when explicitly enabled.
self.queries_log = deque(maxlen=self.queries_limit)
}}}
This means that if the queries log hits 9K entries, `assertNumQueries`
will no longer see there as being any new queries, and will return 0 for
the `captured_queries`, which is rather tricky to debug.
The minimal solution would be for `CaptureQueriesContext` to check if
`self.initial_queries` is >= than `queries_limit` and noisily fail if so,
since the test won't work if it is.
I don't yet have a better solution....
--
Ticket URL: <https://code.djangoproject.com/ticket/27539>
Django <https://code.djangoproject.com/>
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