test(medgemma): add tests for Gemma chat template formatting

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

trialpath/tests/test_medgemma.py

@@ -90,6 +90,27 @@ class TestMedGemmaExtraction:
         assert "65" in prompt
         assert "male" in prompt
 
+    def test_format_gemma_prompt_basic(self):
+        """_format_gemma_prompt should produce valid Gemma chat template."""
+        extractor = MedGemmaExtractor.__new__(MedGemmaExtractor)
+        messages = [
+            {"role": "system", "content": "You are an oncology expert."},
+            {"role": "user", "content": "Extract the diagnosis."},
+        ]
+        result = extractor._format_gemma_prompt(messages)
+        assert "<start_of_turn>user" in result
+        assert "You are an oncology expert." in result
+        assert "Extract the diagnosis." in result
+        assert result.endswith("<start_of_turn>model\n")
+
+    def test_format_gemma_prompt_no_system(self):
+        """_format_gemma_prompt should work without system message."""
+        extractor = MedGemmaExtractor.__new__(MedGemmaExtractor)
+        messages = [{"role": "user", "content": "Hello"}]
+        result = extractor._format_gemma_prompt(messages)
+        assert "<start_of_turn>user\nHello<end_of_turn>" in result
+        assert "<start_of_turn>model\n" in result
+
 
 class TestMedGemmaHFEndpoint:
     """Test HF Inference Endpoint integration."""