diff --git a/tests/basic/test_sendchat.py b/tests/basic/test_sendchat.py
index fb2b6fb5a..815aba282 100644
--- a/tests/basic/test_sendchat.py
+++ b/tests/basic/test_sendchat.py
@@ -93,3 +93,74 @@ class TestSendChat(unittest.TestCase):
         assert result is None
         # Should only print the error message
         assert mock_print.call_count == 1
+
+    def test_ensure_alternating_roles_empty(self):
+        from aider.sendchat import ensure_alternating_roles
+        messages = []
+        result = ensure_alternating_roles(messages)
+        assert result == []
+
+    def test_ensure_alternating_roles_single_message(self):
+        from aider.sendchat import ensure_alternating_roles
+        messages = [{"role": "user", "content": "Hello"}]
+        result = ensure_alternating_roles(messages)
+        assert result == messages
+
+    def test_ensure_alternating_roles_already_alternating(self):
+        from aider.sendchat import ensure_alternating_roles
+        messages = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": "Hi there"},
+            {"role": "user", "content": "How are you?"},
+        ]
+        result = ensure_alternating_roles(messages)
+        assert result == messages
+
+    def test_ensure_alternating_roles_consecutive_user(self):
+        from aider.sendchat import ensure_alternating_roles
+        messages = [
+            {"role": "user", "content": "Hello"},
+            {"role": "user", "content": "Are you there?"},
+        ]
+        expected = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": ""},
+            {"role": "user", "content": "Are you there?"},
+        ]
+        result = ensure_alternating_roles(messages)
+        assert result == expected
+
+    def test_ensure_alternating_roles_consecutive_assistant(self):
+        from aider.sendchat import ensure_alternating_roles
+        messages = [
+            {"role": "assistant", "content": "Hi there"},
+            {"role": "assistant", "content": "How can I help?"},
+        ]
+        expected = [
+            {"role": "assistant", "content": "Hi there"},
+            {"role": "user", "content": ""},
+            {"role": "assistant", "content": "How can I help?"},
+        ]
+        result = ensure_alternating_roles(messages)
+        assert result == expected
+
+    def test_ensure_alternating_roles_mixed_sequence(self):
+        from aider.sendchat import ensure_alternating_roles
+        messages = [
+            {"role": "user", "content": "Hello"},
+            {"role": "user", "content": "Are you there?"},
+            {"role": "assistant", "content": "Yes"},
+            {"role": "assistant", "content": "How can I help?"},
+            {"role": "user", "content": "Write code"},
+        ]
+        expected = [
+            {"role": "user", "content": "Hello"},
+            {"role": "assistant", "content": ""},
+            {"role": "user", "content": "Are you there?"},
+            {"role": "assistant", "content": "Yes"},
+            {"role": "user", "content": ""},
+            {"role": "assistant", "content": "How can I help?"},
+            {"role": "user", "content": "Write code"},
+        ]
+        result = ensure_alternating_roles(messages)
+        assert result == expected