[IMP] tests: allow to add a margin on performance tests

Purpose of this commit is to avoid errors for some performance tests that
have a slightly variable number of queries. Indeed some tests in test_mail
module vary of 1 or 2 queries due to a behavior still not found that does
not seem deterministic.

This should not be considered as a real error, but should not be considered
as completely valid. This is why a margin is accepted in some tests that
will raise a warning instead of an error. This warning tells people to
check if they have increased the query counter or if it is due to a random
effect in query count.

0 files changed, 0 insertions, 0 deletions