diff --git a/tests/test-bad-extension.t b/tests/test-bad-extension.t
--- a/tests/test-bad-extension.t
+++ b/tests/test-bad-extension.t
@@ -53,7 +53,8 @@
 
   $ hg -q help help 2>&1 |grep extension
   *** failed to import extension "badext" from $TESTTMP/badext.py: bit bucket overflow
-  *** failed to import extension "badext2": No module named 'badext2'
+  *** failed to import extension "badext2": No module named 'badext2' (py3 !)
+  *** failed to import extension "badext2": No module named badext2 (no-py3 !)
 
 show traceback
 
@@ -61,7 +62,8 @@
   *** failed to import extension "badext" from $TESTTMP/badext.py: bit bucket overflow
   Traceback (most recent call last):
   Exception: bit bucket overflow
-  *** failed to import extension "badext2": No module named 'badext2'
+  *** failed to import extension "badext2": No module named 'badext2' (py3 !)
+  *** failed to import extension "badext2": No module named badext2 (no-py3 !)
   Traceback (most recent call last):
   ImportError: No module named badext2 (no-py3 !)
   ImportError: No module named 'hgext.badext2' (py3 no-py36 !)
@@ -123,7 +125,8 @@
   Traceback (most recent call last): (py3 !)
   ImportError: No module named 'hgext3rd.badext2' (py3 no-py36 !)
   ModuleNotFoundError: No module named 'hgext3rd.badext2' (py36 !)
-  *** failed to import extension "badext2": No module named 'badext2'
+  *** failed to import extension "badext2": No module named 'badext2' (py3 !)
+  *** failed to import extension "badext2": No module named badext2 (no-py3 !)
   Traceback (most recent call last):
   ImportError: No module named 'hgext.badext2' (py3 no-py36 !)
   ModuleNotFoundError: No module named 'hgext.badext2' (py36 !)
@@ -161,7 +164,8 @@
 
   $ hg help --keyword baddocext
   *** failed to import extension "badext" from $TESTTMP/badext.py: bit bucket overflow
-  *** failed to import extension "badext2": No module named 'badext2'
+  *** failed to import extension "badext2": No module named 'badext2' (py3 !)
+  *** failed to import extension "badext2": No module named badext2 (no-py3 !)
   Topics:
   
    extensions Using Additional Features
diff --git a/tests/test-extension.t b/tests/test-extension.t
--- a/tests/test-extension.t
+++ b/tests/test-extension.t
@@ -649,7 +649,7 @@
 module stub. Our custom lazy importer for Python 2 always returns a stub.
 
   $ (PYTHONPATH=${PYTHONPATH}${PATHSEP}${TESTTMP}; hg --config extensions.checkrelativity=$TESTTMP/checkrelativity.py checkrelativity) || true
-  *** failed to import extension "checkrelativity" from $TESTTMP/checkrelativity.py: No module named 'extlibroot.lsub1.lsub2.notexist'
+  *** failed to import extension "checkrelativity" from $TESTTMP/checkrelativity.py: No module named 'extlibroot.lsub1.lsub2.notexist' (py3 !)
   hg: unknown command 'checkrelativity' (py3 !)
   (use 'hg help' for a list of commands) (py3 !)
 
@@ -1939,7 +1939,8 @@
   > test_unicode_default_value = $TESTTMP/test_unicode_default_value.py
   > EOF
   $ hg -R $TESTTMP/opt-unicode-default dummy
-  *** failed to import extension "test_unicode_default_value" from $TESTTMP/test_unicode_default_value.py: unicode 'value' found in cmdtable.dummy
+  *** failed to import extension "test_unicode_default_value" from $TESTTMP/test_unicode_default_value.py: unicode 'value' found in cmdtable.dummy (py3 !)
+  *** failed to import extension "test_unicode_default_value" from $TESTTMP/test_unicode_default_value.py: unicode u'value' found in cmdtable.dummy (no-py3 !)
   *** (use b'' to make it byte string)
   hg: unknown command 'dummy'
   (did you mean summary?)