Merge pull request #4032 from hjwp/patch-1

add documentation of register_assert_rewrite

Author: nicoddemus

doc/en/assert.rst

@@ -264,8 +264,12 @@ Advanced assertion introspection
 Reporting details about a failing assertion is achieved by rewriting assert
 statements before they are run.  Rewritten assert statements put introspection
 information into the assertion failure message.  ``pytest`` only rewrites test
-modules directly discovered by its test collection process, so asserts in
-supporting modules which are not themselves test modules will not be rewritten.
+modules directly discovered by its test collection process, so **asserts in
+supporting modules which are not themselves test modules will not be rewritten**.
+
+You can manually enable assertion rewriting for an imported module by calling
+`register_assert_rewrite <https://docs.pytest.org/en/latest/writing_plugins.html#assertion-rewriting>`_
+before you import it (a good place to do that is in ``conftest.py``).
 
 .. note::