Linker error is being generated when I try to generate a seperate binary for tests only

Code
1

Error message:

/usr/bin/ld: CMakeFiles/test.dir/test_lexer.c.o: in function `test_next_token':
test_lexer.c:(.text+0x11f): undefined reference to `lexer_create'
/usr/bin/ld: test_lexer.c:(.text+0x144): undefined reference to `lexer_next_token'
/usr/bin/ld: test_lexer.c:(.text+0x1d7): undefined reference to `lexer_destroy'
collect2: error: ld returned 1 exit status
make[2]: *** [test/CMakeFiles/test.dir/build.make:98: test/test] Error 1
make[1]: *** [CMakeFiles/Makefile2:143: test/CMakeFiles/test.dir/all] Error 2
make: *** [Makefile:136: all] Error 2

File structure

.  
├── CMakeLists.txt
├── include
│   ├── lexer.h
│   └── token.h
├── LICENSE
├── README.md
├── src
│   ├── lexer.c
│   ├── main.c
│   └── token.c
└── test
    ├── CMakeLists.txt
    └── test_lexer.c

./CMakeLists.txt

cmake_minimum_required(VERSION 3.25)
project(monkeylang)

set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

include_directories(include)

link_directories(test)

add_subdirectory(test)

add_executable(${PROJECT_NAME} 
    src/main.c
    src/lexer.c
    src/token.c
    include/lexer.h
    include/token.h
)

test/CMakeLists.txt

cmake_minimum_required(VERSION 3.25)
project(test)

set(CMAKE_C_STANDARD 99)
set(CMAKE_EXPORT_COMPILE_COMMANDS ON)

include(FetchContent)

FetchContent_Declare(
    unity
    GIT_REPOSITORY https://github.com/ThrowTheSwitch/Unity.git
    GIT_TAG v2.6.0
)

FetchContent_MakeAvailable(unity)

add_executable(${PROJECT_NAME} test_lexer.c)

target_link_libraries(${PROJECT_NAME} unity)

I want to generate a seperate binary for testing only, but a linker error occurs when I try to reference function definitions from include/ and src , Any idea how to resolve this?

2

From what I see, the test target doesn’t link to anything that compiles those sources, so that error is to be expected. You could link to monkeylang target (if its sources contain the symbols you need in test), although it isn’t very usual to link to executables; or perhaps you could make a library and link to that instead.