add more unit test.

gnmi_server/server_test.go

@@ -2961,6 +2961,33 @@ func TestGNOI(t *testing.T) {
 		}
 	})
 
+	t.Run("OSVerifyFailure", func(t *testing.T) {
+		mockClient := &ssc.DbusClient{}
+		expectedError := fmt.Errorf("failed to verify OS")
+
+		mock := gomonkey.ApplyMethod(reflect.TypeOf(mockClient), "ListImages", func(_ *ssc.DbusClient) (string, error) {
+			return "", expectedError
+		})
+		defer mock.Reset()
+
+		// Prepare context and request
+		ctx := context.Background()
+		req := &gnoi_os_pb.VerifyRequest{}
+		osc := gnoi_os_pb.NewOSClient(conn)
+
+		resp, err := osc.Verify(ctx, req)
+		if err == nil {
+			t.Fatalf("Expected error but got none")
+		}
+		if resp != nil {
+			t.Fatalf("Expected nil response but got: %v", resp)
+		}
+
+		if !strings.Contains(err.Error(), expectedError.Error()) {
+			t.Errorf("Expected error to contain '%v' but got '%v'", expectedError, err)
+		}
+	})
+
 	type configData struct {
 		source      string
 		destination string