cmake --build <path> --target help does not list the "tests" target when using Ninja generator

[alexwpitt]

The "help" target is used to check if a particular target exists:

colcon-cmake/colcon_cmake/task/cmake/__init__.py

Lines 92 to 93 in 2e824fd

	output = subprocess.check_output([
	CMAKE_EXECUTABLE, '--build', path, '--target', 'help'], cwd=path)

But when using the Ninja generator, the "tests" target does not seem to appear in the output of that command, and therefore is not built by a colcon build on a ROS package containing cmake such as:

if(CATKIN_ENABLE_TESTING)
  find_package(rostest REQUIRED)
  add_rostest_gtest(dummy_node_test test/dummy_node.test test/DummyNodeTest.cpp)
  target_include_directories(dummy_node_test SYSTEM PRIVATE ${catkin_INCLUDE_DIRS})
  target_link_libraries(dummy_node_test ${catkin_LIBRARIES})
endif()

This causes colcon test failures if rostest tries to launch the unbuilt test binary.