How to add include_directory in simple CMake Project - cmake

Question

I have CMake project whose directory structure is as follows:
├── build
├── CMakeLists.txt
├── src
│   ├── CMakeLists.txt
│   ├── headers
│   │   └── utility.h
│   └── main.cpp
└── tests
├── CMakeLists.txt
├── testfeature_a
│   ├── CMakeLists.txt
│   └── test_me.cpp
└── test_main.cpp
In test_me.cpp I wanted to include utility.h as I wanted to test functions defined there. So I did #include "headers/utility.h" and in testfeature_a CMakeLists.txt I did this:
file(GLOB SRCS *.cpp)
ADD_EXECUTABLE(testfeature_a ${SRCS})
include_directories(src/headers)
TARGET_LINK_LIBRARIES(
testfeature_a
libgtest
libgmock
)
add_test(NAME testfeature_a
COMMAND testfeature_a)
But the make fails with the error message fatal error: headers/utility.h: No such file or directory.
How can I include the headers directory in test_me.cpp

Answer 1

Your path in include_directories() may be incorrect. Here are two things that you could check
The file seems to be the CMakeLists.txt in tests-folder so you need to go up one folder before you can go to src-folder, i.e. include_directories(../src/headers).
You repeat the headers-folder in the #include "headers/utility.h" when you have already specified it in include_directories(src/headers). Either use #include "utility.h" in cpp-file or include_directories(src) in CMakeLists.txt.
Other option is that you don't need to specify the headers-folder in the CMakeLists.txt at all. You can simply use #include "path/to/your/file.h without any other configuration.
For debugging your path in the CMakeLists.txt you can call message-function, e.g. message(${your_path}), so it's printed when executed and you can check if it's correct.
In addition you can use CMake built-in variables such as CMAKE_CURRENT_SOURCE_DIR and CMAKE_SOURCE_DIR, e.g. include_directories(${CMAKE_SOURCE_DIR}/src/headers)