diff --git a/src/semantic-router/pkg/extproc/reason_mode_selector_test.go b/src/semantic-router/pkg/extproc/reason_mode_selector_test.go
new file mode 100644
index 00000000..a58eead1
--- /dev/null
+++ b/src/semantic-router/pkg/extproc/reason_mode_selector_test.go
@@ -0,0 +1,71 @@
+package extproc
+
+import "testing"
+
+// TestGetModelFamilyAndTemplateParam verifies model-family detection and template parameter mapping
+func TestGetModelFamilyAndTemplateParam(t *testing.T) {
+	testCases := []struct {
+		name           string
+		model          string
+		expectedFamily string
+		expectedParam  string
+	}{
+		{
+			name:           "Qwen3 family",
+			model:          "Qwen3-7B",
+			expectedFamily: "qwen3",
+			expectedParam:  "enable_thinking",
+		},
+		{
+			name:           "DeepSeek family",
+			model:          "deepseek-v31",
+			expectedFamily: "deepseek",
+			expectedParam:  "thinking",
+		},
+		{
+			name:           "DeepSeek alias ds",
+			model:          "DS-1.5B",
+			expectedFamily: "deepseek",
+			expectedParam:  "thinking",
+		},
+		{
+			name:           "GPT-OSS family",
+			model:          "gpt-oss-20b",
+			expectedFamily: "gpt-oss",
+			expectedParam:  "reasoning_effort",
+		},
+		{
+			name:           "GPT generic family",
+			model:          "gpt-4o-mini",
+			expectedFamily: "gpt",
+			expectedParam:  "reasoning_effort",
+		},
+		{
+			name:           "GPT underscore variant",
+			model:          "  GPT_OSS-foo  ",
+			expectedFamily: "gpt-oss",
+			expectedParam:  "reasoning_effort",
+		},
+		{
+			name:           "Unknown family",
+			model:          "phi4",
+			expectedFamily: "unknown",
+			expectedParam:  "",
+		},
+		{
+			name:           "Empty model name",
+			model:          "",
+			expectedFamily: "unknown",
+			expectedParam:  "",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			family, param := getModelFamilyAndTemplateParam(tc.model)
+			if family != tc.expectedFamily || param != tc.expectedParam {
+				t.Fatalf("for model %q got (family=%q, param=%q), want (family=%q, param=%q)", tc.model, family, param, tc.expectedFamily, tc.expectedParam)
+			}
+		})
+	}
+}