diff --git a/tests/test_cliutil.py b/tests/test_cliutil.py
index 08cddf36c92ef980a362624b2451df9655fba289..c1314c8055ff18e08b5f6d92c6d7231af7cca107 100644
--- a/tests/test_cliutil.py
+++ b/tests/test_cliutil.py
@@ -27,6 +27,11 @@ import pytest
 
 from conservancy_beancount import cliutil
 
+class AlwaysEqual:
+    def __eq__(self, other):
+        return True
+
+
 class MockTraceback:
     def __init__(self, stack=None, index=0):
         if stack is None:
@@ -91,8 +96,12 @@ def test_excepthook_traceback(caplog):
     assert caplog.records
     assert caplog.records[-1].message == ''.join(traceback.format_exception(*args))
 
-def test_is_main_script():
-    assert not cliutil.is_main_script()
+@pytest.mark.parametrize('prog_name,expected', [
+    ('', False),
+    (AlwaysEqual(), True),
+])
+def test_is_main_script(prog_name, expected):
+    assert cliutil.is_main_script(prog_name) == expected
 
 @pytest.mark.parametrize('arg,expected', [
     ('debug', logging.DEBUG),