Proper escaping of % in string literals used when defining constaints
was attempted (a8b3f96f6) by overriding quote_value of Postgres and
Oracle schema editor. The same approach was used when adding support for
constraints to the MySQL/MariaDB backend (1fc2c70).
Later on it was discovered that this approach was not appropriate and
that a preferable one was to pass params=None when executing the
constraint creation DDL to avoid any form of interpolation in the first
place (42e8cf47).
When the second patch was applied the corrective of the first were not
removed which caused % literals to be unnecessary doubled. This flew
under the radar because the existings test were crafted in a way that
consecutive %% didn't catch regressions.
This commit introduces an extra test for __exact lookups which
highlights more adequately % doubling problems but also adjust a
previous __endswith test to cover % doubling problems (%\% -> %%\%%).
Thanks Thomas Kolar for the report.
Refs #32369, #30408, #30593.
To run the test suite, first, create and activate a virtual environment. Then
install some requirements and run the tests::
$ cd tests
$ python -m pip install -e ..
$ python -m pip install -r requirements/py3.txt
$ ./runtests.py
For more information about the test suite, see
https://docs.djangoproject.com/en/dev/internals/contributing/writing-code/unit-tests/.
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