Fixed #24118 -- Added --debug-sql option for tests.

Added a --debug-sql option for tests and runtests.py which outputs the
SQL logger for failing tests. When combined with --verbosity=2, it also
outputs the SQL for passing tests.

Thanks to Berker, Tim, Markus, Shai, Josh and Anssi for review and
discussion.

docs/internals/contributing/writing-code/unit-tests.txt

@@ -286,7 +286,7 @@ For example, suppose that the failing test that works on its own is
 
 .. code-block:: bash
 
-   $ ./runtests.py --bisect basic.tests.ModelTest.test_eq
+    $ ./runtests.py --bisect basic.tests.ModelTest.test_eq
 
 will try to determine a test that interferes with the given one. First, the
 test is run with the first half of the test suite. If a failure occurs, the
@@ -302,7 +302,7 @@ failure. So:
 
 .. code-block:: bash
 
-   $ ./runtests.py --pair basic.tests.ModelTest.test_eq
+    $ ./runtests.py --pair basic.tests.ModelTest.test_eq
 
 will pair ``test_eq`` with every test label.
 
@@ -313,7 +313,7 @@ the first one:
 
 .. code-block:: bash
 
-   $ ./runtests.py --pair basic.tests.ModelTest.test_eq queries transactions
+    $ ./runtests.py --pair basic.tests.ModelTest.test_eq queries transactions
 
 You can also try running any set of tests in reverse using the ``--reverse``
 option in order to verify that executing tests in a different order does not
@@ -321,8 +321,16 @@ cause any trouble:
 
 .. code-block:: bash
 
-   $ ./runtests.py basic --reverse
+    $ ./runtests.py basic --reverse
+
+If you wish to examine the SQL being run in failing tests, you can turn on
+:ref:`SQL logging <django-db-logger>` using the ``--debug-sql`` option. If you
+combine this with ``--verbosity=2``, all SQL queries will be output.
+
+.. code-block:: bash
+
+    $ ./runtests.py basic --debug-sql
 
 .. versionadded:: 1.8
 
-    The ``--reverse`` option was added.
+    The ``--reverse`` and ``--debug-sql`` options were added.

docs/ref/django-admin.txt

@@ -1449,6 +1449,14 @@ This may help in debugging tests that aren't properly isolated and have side
 effects. :ref:`Grouping by test class <order-of-tests>` is preserved when using
 this option.
 
+.. django-admin-option:: --debug-sql
+
+.. versionadded:: 1.8
+
+The ``--debug-sql`` option can be used to enable :ref:`SQL logging
+<django-db-logger>` for failing tests. If :djadminopt:`--verbosity` is ``2``,
+then queries in passing tests are also output.
+
 testserver <fixture fixture ...>
 --------------------------------
 

docs/releases/1.8.txt

@@ -625,8 +625,9 @@ Tests
   allows you to test that two JSON fragments are not equal.
 
 * Added options to the :djadmin:`test` command to preserve the test database
-  (:djadminopt:`--keepdb`) and to run the test cases in reverse order
-  (:djadminopt:`--reverse`).
+  (:djadminopt:`--keepdb`), to run the test cases in reverse order
+  (:djadminopt:`--reverse`), and to enable SQL logging for failing tests
+  (:djadminopt:`--debug-sql`).
 
 * Added the :attr:`~django.test.Response.resolver_match` attribute to test
   client responses.

docs/topics/logging.txt

@@ -439,6 +439,8 @@ Messages to this logger have the following extra context:
 * ``request``: The request object that generated the logging
   message.
 
+.. _django-db-logger:
+
 ``django.db.backends``
 ~~~~~~~~~~~~~~~~~~~~~~
 

docs/topics/testing/advanced.txt

@@ -355,7 +355,7 @@ behavior. This class defines the ``run_tests()`` entry point, plus a
 selection of other methods that are used to by ``run_tests()`` to set up,
 execute and tear down the test suite.
 
-.. class:: DiscoverRunner(pattern='test*.py', top_level=None, verbosity=1, interactive=True, failfast=True, keepdb=False, reverse=False, **kwargs)
+.. class:: DiscoverRunner(pattern='test*.py', top_level=None, verbosity=1, interactive=True, failfast=True, keepdb=False, reverse=False, debug_sql=False, **kwargs)
 
     ``DiscoverRunner`` will search for tests in any file matching ``pattern``.
 
@@ -386,6 +386,11 @@ execute and tear down the test suite.
     and have side effects. :ref:`Grouping by test class <order-of-tests>` is
     preserved when using this option.
 
+    If ``debug_sql`` is ``True``, failing test cases will output SQL queries
+    logged to the :ref:`django.db.backends logger <django-db-logger>` as well
+    as the traceback. If ``verbosity`` is ``2``, then queries in all tests are
+    output.
+
     Django may, from time to time, extend the capabilities of the test runner
     by adding new arguments. The ``**kwargs`` declaration allows for this
     expansion. If you subclass ``DiscoverRunner`` or write your own test
@@ -402,7 +407,7 @@ execute and tear down the test suite.
         subclassed test runner to add options to the list of command-line
         options that the :djadmin:`test` command could use.
 
-        The ``keepdb`` and the ``reverse`` arguments were added.
+        The ``keepdb``, ``reverse``, and ``debug_sql`` arguments were added.
 
 Attributes
 ~~~~~~~~~~