cmake_minimum_required(VERSION 3.4)

project(Foo NONE)

add_custom_target(foo ALL)

file(WRITE test.cmake [[
    message("Hello World")
    execute_process(COMMAND ${CMAKE_COMMAND} -E sleep 60)
]])

add_custom_command(TARGET foo
    COMMAND ${CMAKE_COMMAND} -P ${CMAKE_SOURCE_DIR}/test.cmake
    VERBATIM
    USES_TERMINAL
)