[tests] use subTest with l10n_tests.TestSites

Change-Id: If8565af684434d0a48f9aa1187739491f0d1e80a
---
M tests/l10n_tests.py
1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/tests/l10n_tests.py b/tests/l10n_tests.py
index 2b86318..f461ee3 100644
--- a/tests/l10n_tests.py
+++ b/tests/l10n_tests.py
@@ -107,9 +107,10 @@
         for package in PACKAGES:
             keys = i18n.twget_keys(package)
             for key in keys:
-                self.assertIn(key, languages,
-                              "'{}' - json key '{}' is not a site language"
-                              .format(package, key))
+                with self.subTest(package=package, key=key):
+                    self.assertIn(key, languages,
+                                  "'{}' - json key '{}' is not a site language"
+                                  .format(package, key))
 
 
 def setUpModule():  # noqa: N802

