diff --git a/tests/end2end/test_invocations.py b/tests/end2end/test_invocations.py
index d34859410..840465704 100644
--- a/tests/end2end/test_invocations.py
+++ b/tests/end2end/test_invocations.py
@@ -110,3 +110,16 @@ def test_no_loglines(quteproc_new):
     quteproc_new.start(args=['--temp-basedir', '--loglines=0'] + BASE_ARGS)
     quteproc_new.open_path('qute:log')
     assert quteproc_new.get_content() == 'Log output was disabled.'
+
+
+@pytest.mark.parametrize('level', ['1', '2'])
+def test_optimize(quteproc_new, capfd, level):
+    quteproc_new.start(args=['--temp-basedir'] + BASE_ARGS,
+                       env={'PYTHONOPTIMIZE': level})
+    if level == '2':
+        msg = ("Running on optimize level higher than 1, unexpected behavior "
+               "may occur.")
+        line = quteproc_new.wait_for(message=msg)
+        line.expected = True
+    quteproc_new.send_cmd(':quit')
+    quteproc_new.wait_for_quit()
diff --git a/tests/unit/commands/test_cmdutils.py b/tests/unit/commands/test_cmdutils.py
index 1ecdbaf3a..cd074cbcd 100644
--- a/tests/unit/commands/test_cmdutils.py
+++ b/tests/unit/commands/test_cmdutils.py
@@ -21,6 +21,10 @@
 
 """Tests for qutebrowser.commands.cmdutils."""
 
+import sys
+import logging
+import types
+
 import pytest
 
 from qutebrowser.commands import cmdutils, cmdexc, argparser, command
@@ -354,6 +358,24 @@ class TestArgument:
 
         assert str(excinfo.value) == "Argument marked as both count/win_id!"
 
+    def test_no_docstring(self, caplog):
+        with caplog.at_level(logging.WARNING):
+            @cmdutils.register()
+            def fun():
+                # no docstring
+                pass
+        assert len(caplog.records) == 1
+        msg = caplog.records[0].message
+        assert msg.endswith('test_cmdutils.py has no docstring')
+
+    def test_no_docstring_with_optimize(self, monkeypatch):
+        """With -OO we'd get a warning on start, but no warning afterwards."""
+        monkeypatch.setattr(sys, 'flags', types.SimpleNamespace(optimize=2))
+        @cmdutils.register()
+        def fun():
+            # no docstring
+            pass
+
 
 class TestRun: