diff --git a/tests/commands/hook_impl_test.py b/tests/commands/hook_impl_test.py
index 3e20874e3..aa321dabc 100644
--- a/tests/commands/hook_impl_test.py
+++ b/tests/commands/hook_impl_test.py
@@ -154,6 +154,42 @@ def test_run_ns_commit_msg():
     assert ns.commit_msg_filename == '.git/COMMIT_MSG'
 
 
+def test_run_ns_prepare_commit_msg_one_arg():
+    ns = hook_impl._run_ns(
+        'prepare-commit-msg', False,
+        ('.git/COMMIT_MSG',), b'',
+    )
+    assert ns is not None
+    assert ns.hook_stage == 'prepare-commit-msg'
+    assert ns.color is False
+    assert ns.commit_msg_filename == '.git/COMMIT_MSG'
+
+
+def test_run_ns_prepare_commit_msg_two_arg():
+    ns = hook_impl._run_ns(
+        'prepare-commit-msg', False,
+        ('.git/COMMIT_MSG', 'message'), b'',
+    )
+    assert ns is not None
+    assert ns.hook_stage == 'prepare-commit-msg'
+    assert ns.color is False
+    assert ns.commit_msg_filename == '.git/COMMIT_MSG'
+    assert ns.prepare_commit_message_source == 'message'
+
+
+def test_run_ns_prepare_commit_msg_three_arg():
+    ns = hook_impl._run_ns(
+        'prepare-commit-msg', False,
+        ('.git/COMMIT_MSG', 'message', 'HEAD'), b'',
+    )
+    assert ns is not None
+    assert ns.hook_stage == 'prepare-commit-msg'
+    assert ns.color is False
+    assert ns.commit_msg_filename == '.git/COMMIT_MSG'
+    assert ns.prepare_commit_message_source == 'message'
+    assert ns.commit_object_name == 'HEAD'
+
+
 def test_run_ns_post_commit():
     ns = hook_impl._run_ns('post-commit', True, (), b'')
     assert ns is not None
diff --git a/tests/commands/run_test.py b/tests/commands/run_test.py
index 085b063f3..2634c0c5e 100644
--- a/tests/commands/run_test.py
+++ b/tests/commands/run_test.py
@@ -810,7 +810,12 @@ def test_prepare_commit_msg_hook(cap_out, store, prepare_commit_msg_repo):
         cap_out,
         store,
         prepare_commit_msg_repo,
-        {'hook_stage': 'prepare-commit-msg', 'commit_msg_filename': filename},
+        {
+            'hook_stage': 'prepare-commit-msg',
+            'commit_msg_filename': filename,
+            'prepare_commit_message_source': 'commit',
+            'commit_object_name': 'HEAD',
+        },
         expected_outputs=[b'Add "Signed off by:"', b'Passed'],
         expected_ret=0,
         stage=False,