CMake project with a static lib depending on another static lib - c++

Question

I have a project with the below structure. Basically, there are two static libraries: lib_a and lib_b. lib_a uses classes and functions defined in lib_b. There is the main executable, which depends on lib_a (and indirectly on lib_b), and unit tests for lib_a, which also indirectly depend on lib_b.
project
|--CMakeLists.txt
|--static_lib_a
| |--CMakeLists.txt
| |--include
| | \--header_a.h
| \--src
| |--file_a.h
| \--file_a.cpp
|--static_lib_b
| |--CMakeLists.txt
| |--include
| | \--header_b.h
| \--src
| |--file_b.h
| \--file_b.cpp
|--main_exe
| |--CMakeLists.txt
| \--main.cpp
\--unit_test
|--CMakeLists.txt
|--main.cpp
\--test_lib_a.cpp
Since static libraries generally do not link with each other, both main_exe and unit_test need to link lib_a and lib_b. Is there a way to tell CMake that anything that links lib_a also needs to link with lib_b, without specifying this explicitly in main_exe and unit_test? That is, can I express this dependency in static_lib_a/CMakeLists.txt file?
What should be the content of each of the CMakeLists.txt file?
So far I have the following, which produces linking errors (that is, lib_b does not get linked to unit_test):
project/CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
project(project)
enable_testing()
add_subdirectory(static_lib_a)
add_subdirectory(static_lib_b)
add_subdirectory(main_exe)
add_subdirectory(unit_test)
project/static_lib_a/CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
add_library(lib_a STATIC)
target_sources(lib_a PRIVATE
src/file_a.cpp)
target_include_directories(lib_a
PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include
PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)
target_link_libraries(lib_a lib_b)
project/static_lib_b/CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
add_library(lib_b STATIC)
target_sources(lib_b PRIVATE
src/file_b.cpp)
target_include_directories(lib_b
PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include
PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)
main_exe/CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
add_executable(main_exe)
target_sources(main_exe PRIVATE main.cpp)
target_link_libraries(main_exe PRIVATE lib_a)
unit_test/CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
include(CTest)
add_executable(unit_test)
target_sources(unit_test PRIVATE
main.cpp
test_lib_a.cpp)
target_link_libraries(unit_test PRIVATE lib_a)
add_test(NAME unit_test COMMAND unit_test)
add_custom_target(run_unit_test ALL
COMMAND ${CMAKE_CTEST_COMMAND} -C debug --output-on-failure
DEPENDS unit_test)