message: gtest: Qualify nmea_gps test with nmea_gps target
  Change the unit test CMakeLists to only build the nmea_gps unit test if
  the nmea_gps target exists.
diff: @@ -11,22 +11,25 @@ endif()
  add_executable(utilities_tests utilities/utilities_tests.cxx)
  target_link_libraries(utilities_tests utilities GTest::GTest GTest::Main)
  gtest_add_tests(utilities_tests "" AUTO)
  +list(APPEND GTEST_UNIT_TEST_TARGETS utilities_tests)
  # Unit tests - Json header
  add_executable(json_tests json/json_tests.cxx)
  target_link_libraries(json_tests GTest::GTest GTest::Main)
  target_include_directories(json_tests PRIVATE "${UPM_COMMON_HEADER_DIRS}/")
  gtest_add_tests(json_tests "" AUTO)
  +list(APPEND GTEST_UNIT_TEST_TARGETS json_tests)
  # Unit tests - nmea_gps library
  +if (TARGET nmea_gps)
  add_executable(nmea_gps_tests nmea_gps/nmea_gps_tests.cxx)
  target_link_libraries(nmea_gps_tests nmea_gps GTest::GTest GTest::Main)
  gtest_add_tests(nmea_gps_tests "" AUTO)
  + list(APPEND GTEST_UNIT_TEST_TARGETS nmea_gps_tests)
  +endif()
  # Add a custom target for unit tests
  add_custom_target(tests-unit ALL
  DEPENDS
  - utilities_tests
  - json_tests
  + ${GTEST_UNIT_TEST_TARGETS}
  COMMENT "UPM unit test collection")
  -
  