How to add command after all target is built

My goal is to run all tests with CTest as soon as all test binaries are built. Curretly I have the following CMakeList.txt:

add_library(my_lib SHARED mllib.c)

add_executable(test_suite1 test_suite1.c)
target_link_libraries(test_suite1 my_lib)

add_executable(test_suite2 test_suite2.c)
target_link_libraries(test_suite2 my_lib)

 #... many other suites

enable_testing()
add_test(NAME test_suite1 COMMAND test_suite1)
add_test(NAME test_suite2 COMMAND test_suite2)

Now I want to run the command ctest as soon as all test suite binaries are built. There is a form of add_custom_command:

add_custom_command(
     TARGET test_suite
     POST_BUILD 
     COMMAND ctest
)

The problem is that add_custom_command accepts only 1 target and that would require adding another custom command for each test added which duplicating and weird.

Maybe it is possible to create a fake target depending on all the target? Or some other way...?