The following describes the mapping of some ament_tools options and arguments to the colcon command line interface.

ament build | test

--base-paths BASEPATH
--build-space PATH
--build-base PATH
--install-space PATH
--install-base PATH
CMake configures tests by default. To skip configuring tests use --cmake-args -DBUILD_TESTING=OFF.
-s, --symlink-install
The colcon option --merge-install has the inverse logic.
--start-with PKGNAME
--packages-start PKGNAME
--end-with PKGNAME
--packages-end PKGNAME
--only-packages PKGNAME1 ... PKGNAMEn
--packages-select PKGNAME1 ... PKGNAMEn
--skip-packages PKGNAME1 ... PKGNAMEn
--packages-skip PKGNAME1 ... PKGNAMEn
colcon uses the parallel execution by default. To build packages sequentially use --executor sequential.

ament build

colcon build ...

--cmake-args -D... --
--cmake-args -D... The closing double dash is not necessary anymore. Any CMake arguments which match colcon arguments need to be prefixed with a space. This can be done by quoting each argument with a leading space.
When using this option to pass a target name the substitution is: --cmake-target TARGET. When using this option to control the parallel execution with arguments like -jN the substitution is to use the environment variable MAKEFLAGS.
--cmake-args -G Ninja

ament test

colcon test ...

--ctest-args ... --
--ctest-args ... Any CTest arguments which start with a dash need to be prefixed with a space (see --cmake-args).
--retest-until-fail N
--retest-until-fail N
--retest-until-pass N
--retest-until-pass N

ament test_results

colcon test-result ...

--build-base BASEPATH

Behavioral changes

The colcon test verb performs only the action of running tests. It does not build any packages.

--retest-until-fail with colcon uses pytest-repeat which runs individual tests of a package N+1 times each (the first test N+1 times, then the second test N+1 times, etc). With ament_tools the entire test suite of a package was run up to N+1 times. As a consequence colcon provides a more accurate result since each test that passed has actually run N times. Note that with pytest-repeat, pytest tests are repeated N times regardless of the result of the previous runs; if a test fails it will be repeated N times anyway. This is different from the behavior of a CTest test that will stop being repeated as soon as it fails once.

The location of JUnit test results file for ament_python packages tested with colcon is in <pkg-build>/pytest.xml, whereas with ament_tools it is in <pkg-build>/test_results/<pkgname>/pytest.xunit.xml.