Recompile CMake library for every main file (and consider #define) - c++

Question

I'm working on a Websockets library for C++. My project has the library folder and a tests folder.
The tests folder contains many source files that each is compiled as a stand-alone executable and considered a test. The relevant CMakeLists for it looks like this:
file(GLOB TEST_SOURCES "src/*.cpp")
foreach(file ${TEST_SOURCES})
get_filename_component(_F_NAME ${file} NAME_WE)
add_executable(${_F_NAME} ${file})
target_link_libraries (${_F_NAME} ${CMAKE_THREAD_LIBS_INIT})
target_link_libraries(${_F_NAME} tiny_websockets_lib Catch)
if(WIN32)
target_link_libraries(${_F_NAME} wsock32 ws2_32)
endif()
add_test(NAME ${_F_NAME} COMMAND ${_F_NAME})
endforeach()
Basically for every cpp file in src/ I create a new executable and link to it my library (here called tiny_websockets_lib).
The libraries' CMakeLists.txt looks like this:
file(GLOB_RECURSE tinyws_SOURCES
"src/*.cpp"
)
file(GLOB_RECURSE tinyws_HEADERS
"include/*.h"
"include/*.hpp"
)
include_directories(include/tiny_websockets)
add_library(tiny_websockets_lib STATIC ${tinyws_HEADERS} ${tinyws_SOURCES})
set_target_properties(tiny_websockets_lib PROPERTIES LINKER_LANGUAGE CXX)
target_include_directories(tiny_websockets_lib PUBLIC include)
The Issue:
In the library I have some conditional compilation flags. For example, this flag:
#define _WS_CONFIG_NO_TRUE_RANDOMNESS
can be defined and it will change the behivour of the library.
The problem is that the library only compiles once, so if my test looks like this:
#define _WS_CONFIG_NO_TRUE_RANDOMNESS
#include <library_stuff_with_conditional_compile_ifdefs>
int main() {
// tests
}
The library will not be compiled again, and the flag will not be considered.
TLDR: To my understanding the library is compiled once and linked multiple times. I would like the library to recompile and consider the main file for every tests.
You can see the actual project and structure here: https://github.com/gilmaimon/TinyWebsockets
Thank You.