.c file is not recgnized - c

Question

I cannot build c project.
I am novice of C language, so I can't understand what is problem.
Webstorm setting, or setting of cmake ?
Why I cannot build my projects.
Environment:
Editor: Clion
Created Project from C Executable
Lnaguage standard: C99
Error message
/Applications/CLion.app/Contents/bin/cmake/mac/bin/cmake --build /Users/me/CLionProjects/test/cmake-build-debug --target test -- -j 2
[ 50%] Linking C executable test
Undefined symbols for architecture x86_64:
"_test", referenced from:
_main in main.c.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[3]: *** [test] Error 1
make[2]: *** [CMakeFiles/test.dir/all] Error 2
make[1]: *** [CMakeFiles/test.dir/rule] Error 2
make: *** [test] Error 2
I wrote main.c
#include "header.h"
int main() {
test();
return 0;
}
header.h file
void test();
header.c file
#include "header.h"
void test() {
}
CMakeLists.txt
cmake_minimum_required(VERSION 3.15)
project(test C)
set(CMAKE_C_STANDARD 99)
add_executable(test main.c)
dicrectory structure is like this.
.
├── CMakeLists.txt
├── cmake-build-debug
│   ├── CMakeCache.txt
│   ├── CMakeFiles
│   │   ├── 3.15.3
│   │   │   ├── CMakeCCompiler.cmake
│   │   │   ├── CMakeDetermineCompilerABI_C.bin
│   │   │   ├── CMakeSystem.cmake
│   │   │   └── CompilerIdC
│   │   │   ├── CMakeCCompilerId.c
│   │   │   ├── a.out
│   │   │   └── tmp
│   │   ├── CMakeDirectoryInformation.cmake
│   │   ├── CMakeOutput.log
│   │   ├── CMakeTmp
│   │   ├── Makefile.cmake
│   │   ├── Makefile2
│   │   ├── Progress
│   │   │   ├── 2
│   │   │   └── count.txt
│   │   ├── TargetDirectories.txt
│   │   ├── clion-environment.txt
│   │   ├── clion-log.txt
│   │   ├── cmake.check_cache
│   │   ├── progress.marks
│   │   └── test.dir
│   │   ├── C.includecache
│   │   ├── DependInfo.cmake
│   │   ├── build.make
│   │   ├── cmake_clean.cmake
│   │   ├── depend.internal
│   │   ├── depend.make
│   │   ├── flags.make
│   │   ├── link.txt
│   │   ├── main.c.o
│   │   ├── progress.make
│   │   └── src
│   ├── Makefile
│   ├── cmake_install.cmake
│   └── test.cbp
├── header.c
├── header.h
├── main.c
└── src