Python: Achieve 85%+ unit test coverage for azurefunctions package (#3866)

* Initial plan

* Initial analysis: azurefunctions package at 80% coverage, need 85%

Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>

* Add comprehensive unit tests to achieve 86% coverage for azurefunctions package

Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>

* Add comprehensive coverage report documentation for azurefunctions package

Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>

* Fix linting errors: combine nested with statements in test_entities.py

Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>

* Remove COVERAGE_REPORT.md and coverage.json files as requested

Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>

* Address PR review feedback: fix unused variables, remove line numbers from docstrings, improve test clarity

Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: larohra <41490930+larohra@users.noreply.github.com>
Co-authored-by: Laveesh Rohra <larohra@microsoft.com>
Co-authored-by: Tao Chen <taochen@microsoft.com>

python/packages/azurefunctions/tests/test_app.py

@@ -1164,5 +1164,158 @@ class TestMCPToolEndpoint:
         assert body["agents"][0]["mcp_tool_enabled"] is True
 
 
+class TestAgentFunctionAppErrorPaths:
+    """Test suite for error handling paths."""
+
+    def test_init_with_invalid_max_poll_retries(self) -> None:
+        """Test initialization handles invalid max_poll_retries by falling back to default."""
+        mock_agent = Mock()
+        mock_agent.name = "TestAgent"
+
+        # Test with invalid type
+        app = AgentFunctionApp(agents=[mock_agent], max_poll_retries="invalid")
+        assert app.max_poll_retries >= 1  # Should use default
+
+        # Test with None
+        app2 = AgentFunctionApp(agents=[mock_agent], max_poll_retries=None)
+        assert app2.max_poll_retries >= 1  # Should use default
+
+    def test_init_with_invalid_poll_interval_seconds(self) -> None:
+        """Test initialization handles invalid poll_interval_seconds by falling back to default."""
+        mock_agent = Mock()
+        mock_agent.name = "TestAgent"
+
+        # Test with invalid type
+        app = AgentFunctionApp(agents=[mock_agent], poll_interval_seconds="invalid")
+        assert app.poll_interval_seconds > 0  # Should use default
+
+        # Test with None
+        app2 = AgentFunctionApp(agents=[mock_agent], poll_interval_seconds=None)
+        assert app2.poll_interval_seconds > 0  # Should use default
+
+    def test_get_agent_raises_for_unregistered_agent(self) -> None:
+        """Test get_agent raises ValueError for unregistered agent."""
+        mock_agent = Mock()
+        mock_agent.name = "RegisteredAgent"
+
+        app = AgentFunctionApp(agents=[mock_agent], enable_http_endpoints=False)
+
+        # Create mock orchestration context
+        mock_context = Mock()
+
+        # Should raise ValueError for unregistered agent
+        with pytest.raises(ValueError, match="Agent 'UnknownAgent' is not registered"):
+            app.get_agent(mock_context, "UnknownAgent")
+
+    def test_convert_payload_to_text_with_response_key(self) -> None:
+        """Test _convert_payload_to_text returns response key value."""
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        # Test with response key
+        payload = {"response": "Test response"}
+        result = app._convert_payload_to_text(payload)
+        assert result == "Test response"
+
+        # Test with error key
+        payload = {"error": "Error message"}
+        result = app._convert_payload_to_text(payload)
+        assert result == "Error message"
+
+        # Test with message key
+        payload = {"message": "Message text"}
+        result = app._convert_payload_to_text(payload)
+        assert result == "Message text"
+
+        # Test with no matching keys - should return JSON string
+        payload = {"other": "value"}
+        result = app._convert_payload_to_text(payload)
+        assert "other" in result
+        assert "value" in result
+
+    def test_create_session_id_with_thread_id(self) -> None:
+        """Test _create_session_id with provided thread_id."""
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        # With thread_id provided
+        session_id = app._create_session_id("TestAgent", "my-thread-123")
+        assert session_id.key == "my-thread-123"
+
+        # Without thread_id (None) - should generate random
+        session_id = app._create_session_id("TestAgent", None)
+        assert session_id.key is not None
+        assert len(session_id.key) > 0
+
+    def test_resolve_thread_id_from_body(self) -> None:
+        """Test _resolve_thread_id extracts from body."""
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        mock_req = Mock()
+        mock_req.params = {}
+
+        # Thread ID in body - field name is "thread_id"
+        req_body = {"thread_id": "body-thread-123"}
+        result = app._resolve_thread_id(mock_req, req_body)
+        assert result == "body-thread-123"
+
+    def test_select_body_parser_json_content_type(self) -> None:
+        """Test _select_body_parser for JSON content type."""
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        # Test with application/json
+        parser, format_str = app._select_body_parser("application/json")
+        assert parser == app._parse_json_body
+        assert format_str == "json"
+
+        # Test with +json suffix
+        parser, format_str = app._select_body_parser("application/vnd.api+json")
+        assert parser == app._parse_json_body
+        assert format_str == "json"
+
+    def test_accepts_json_response_with_accept_header(self) -> None:
+        """Test _accepts_json_response checks accept header."""
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        # With application/json in accept header
+        headers = {"accept": "application/json"}
+        result = app._accepts_json_response(headers)
+        assert result is True
+
+        # Without accept header
+        headers = {}
+        result = app._accepts_json_response(headers)
+        assert result is False
+
+    def test_parse_json_body_invalid_type(self) -> None:
+        """Test _parse_json_body raises error for invalid JSON."""
+        from agent_framework_azurefunctions._errors import IncomingRequestError
+
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        # Mock request with non-dict JSON
+        mock_req = Mock()
+        mock_req.get_json.return_value = ["not", "a", "dict"]
+
+        with pytest.raises(IncomingRequestError, match="Invalid JSON payload"):
+            app._parse_json_body(mock_req)
+
+    def test_coerce_to_bool_with_none(self) -> None:
+        """Test _coerce_to_bool handles None and various value types."""
+        app = AgentFunctionApp(enable_http_endpoints=False, enable_health_check=False)
+
+        # None returns False
+        assert app._coerce_to_bool(None) is False
+
+        # Integer
+        assert app._coerce_to_bool(1) is True
+        assert app._coerce_to_bool(0) is False
+
+        # String
+        assert app._coerce_to_bool("true") is True
+        assert app._coerce_to_bool("false") is False
+
+        # Other type returns False
+        assert app._coerce_to_bool([]) is False
+
+
 if __name__ == "__main__":
     pytest.main([__file__, "-v", "--tb=short"])