`ament_add_gtest_test` macro does not ensure `ament_cmake_test` is found

[sea-bass]

I just wrote the following config

# If ament_gtest is detected, make the tests visible in ROS 2.
find_package(ament_cmake_gtest QUIET)
if ( ament_cmake_gtest_FOUND )
    ament_add_gtest_test(test_types)
endif()

When I try to build with this, I get the following error:

CMake Error at /opt/ros/rolling/share/ament_cmake_gtest/cmake/ament_add_gtest_test.cmake:95 (ament_add_test):
  Unknown CMake command "ament_add_test".
Call Stack (most recent call first):
  test/CMakeLists.txt:21 (ament_add_gtest_test)

It appears that the ament_add_gtest_test macro uses ament_add_test internally (see here), but nothing looks for a dependency on the ament_cmake_test package this comes from.

If I add this line

find_package(ament_cmake_test REQUIRED)

to my config, things work as expected... but I think I shouldn't need to do that, right?

[sea-bass]

I think the more "usual" paths work out because when you call ament_add_gtest:

• This internally calls ament_add_gtest_executable
• In turn, this internally calls _ament_cmake_gtest_find_gtest
• Which finally does the find_package(ament_cmake_test QUIET REQUIRED) call as shown below

ament_cmake/ament_cmake_gtest/ament_cmake_gtest-extras.cmake

Line 22 in 2338dec

find_package(ament_cmake_test QUIET REQUIRED)

... but if you do ament_add_gtest_test directly, this is bypassed entirely.

I've updated the issue title.

[Yadunund]

@cottsay please take a look when you get a chance 🧇