specify destination for CTestTestfile.cmake - cmake

Question

When executing cmake to generate ctest inputs, how can I directly specify the destination directory for the cmake-generated CTestTestfile.cmake? Specifically, my test suite is an independent cmake project. I currently add it to the main cmake project with include(), but the more appropriate method is to use add_subdirectory(). However, add_subdirectory() installs CTestTestfile.cmake in the subproject's directory in the build directory, but I need it in build/ for ctest to find it.
I set up the test macros in a file CTestList.cmake which lives in the test_project. This file is included in the build in test_project/CMakeLists.txt:
include(CTest)
include(${CMAKE_CURRENT_LIST_DIR}/CTestList.cmake)
With include():
project/
|-- CMakeLists.txt
|-- src/
|-- test_project/
`-- build/
|-- CTestTestfile.cmake
`-- test_project/
With add_subdirectory():
project/
|-- CMakeLists.txt
|-- src/
|-- test_project/
`-- build/
`-- test_project/
`-- CTestTestfile.cmake

Answer 1

The include and the add_subdirectory commands of CMake are very different.
While the include command works like #include of C and C++ – loads the content of included file into the file where it appears –, the add_subdirectory adds a subdirectory to the build. This means that when you use the add_subdirectory the variables inside the subdirectory's CMakeLists.txt will be the part of a different scope and the value of CMAKE_CURRENT_BINARY_DIR variable will be different too. Just add the following line to the test_project/CMakeLists.txt and try either to include it or add it by add_subdirectory:
message(STATUS "The files will be generated into: " ${CMAKE_CURRENT_BINARY_DIR})
The enable_testing enables testing for current directory and below. So, when you used the add_subdirecory instead of include the current directory meant build/test_project/ – as explained above.
To make sure the CTestTestfile.cmake will be created in build directory too, simply add an extra enable_testing command to the top-level CMakeLists.txt.