From bfbed13737fe3099aef67864a26cd8dd38b30e96 Mon Sep 17 00:00:00 2001
From: Martin Yeo <martin.yeo@metoffice.gov.uk>
Date: Tue, 27 Apr 2021 15:46:46 +0100
Subject: [PATCH] Iris-specific extension to AssertLogs().

---
 lib/iris/tests/__init__.py                    | 25 +++++++++++++++++++
 .../unit/experimental/ugrid/test_Mesh.py      |  4 +--
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/lib/iris/tests/__init__.py b/lib/iris/tests/__init__.py
index b2eebc4f03..2ce9769bcc 100644
--- a/lib/iris/tests/__init__.py
+++ b/lib/iris/tests/__init__.py
@@ -607,6 +607,31 @@ def assertWarnsRegexp(self, expected_regexp=""):
         msg = msg.format(expected_regexp)
         self.assertTrue(matches, msg)
 
+    @contextlib.contextmanager
+    def assertLogs(self, logger=None, level=None):
+        """
+        An extended version of the usual :meth:`unittest.TestCase.assertLogs`,
+        which also exercises the logger's message formatting.
+
+        The inherited version of this method temporarily *replaces* the logger
+        in order to capture log records generated within the context.
+        However, in doing so it prevents any messages from being formatted
+        by the original logger.
+        This version first calls the original method, but then *also* exercises
+        the message formatters of all the logger's handlers, just to check that
+        there are no formatting errors.
+
+        """
+        # Invoke the standard assertLogs behaviour.
+        assertlogging_context = super().assertLogs(logger, level)
+        with assertlogging_context as watcher:
+            # Run the caller context, as per original method.
+            yield watcher
+        # Check for any formatting errors by running all the formatters.
+        for record in watcher.records:
+            for handler in assertlogging_context.logger.handlers:
+                handler.format(record)
+
     @contextlib.contextmanager
     def assertNoWarningsRegexp(self, expected_regexp=""):
         # Check that no warning matching the given expression is raised.
diff --git a/lib/iris/tests/unit/experimental/ugrid/test_Mesh.py b/lib/iris/tests/unit/experimental/ugrid/test_Mesh.py
index a2abb2124f..9b5f4e64e4 100644
--- a/lib/iris/tests/unit/experimental/ugrid/test_Mesh.py
+++ b/lib/iris/tests/unit/experimental/ugrid/test_Mesh.py
@@ -816,7 +816,7 @@ def test_remove_connectivities(self):
         for kwargs in negative_kwargs:
             with self.assertLogs(ugrid.logger, level="DEBUG") as log:
                 # Check that the only debug log is the one we inserted.
-                ugrid.logger.debug("foo")
+                ugrid.logger.debug("foo", extra=dict(cls=None))
                 self.mesh.remove_connectivities(**kwargs)
                 self.assertEqual(1, len(log.records))
             self.assertEqual(self.EDGE_NODE, self.mesh.edge_node_connectivity)
@@ -854,7 +854,7 @@ def test_remove_coords(self):
         for kwargs in negative_kwargs:
             with self.assertLogs(ugrid.logger, level="DEBUG") as log:
                 # Check that the only debug log is the one we inserted.
-                ugrid.logger.debug("foo")
+                ugrid.logger.debug("foo", extra=dict(cls=None))
                 self.mesh.remove_coords(**kwargs)
                 self.assertEqual(1, len(log.records))
             self.assertEqual(self.NODE_LON, self.mesh.node_coords.node_x)