Adds docs and corrects docstring

Author: garry-cairns

Doc/whatsnew/3.15.rst

@@ -274,6 +274,14 @@ typing
   (Contributed by Bénédikt Tran in :gh:`133823`.)
 
 
+unittest
+--------
+* Expose log formatter to users in TestCase.assertLogs.
+  :func:`unittest.TestCase.assertLogs` will now accept a formatter
+  argument so your assertions can match a custom format where you are using one.
+  (Contributed by Garry Cairns in :gh:`134567`.)
+
+
 wave
 ----
 

Lib/unittest/case.py

@@ -861,7 +861,7 @@ def assertLogs(self, logger=None, level=None, formatter=None):
         `records` attribute will be a list of the corresponding LogRecord
         objects.
 
-        Optionally supply `format` to control how messages are formatted.
+        Optionally supply `formatter` to control how messages are formatted.
 
         Example::