CMake unit testing - Unresolved external symbol

I am rather new to C++ and CMake. I’m trying to make a library, and I’m getting the errors when I try to run my unit tests. From my research I’ve already gathered what the "Unresolved external symbol" errors mean, but I’m unable to figure out how to fix it.

Here’s my project structure:

lib
  glfw - GLFW source folder
src
  ogl-renderer.cpp
  ogl-renderer.h
  CMakeLists.txt
  ...additional source files
test
  ogl-test.cpp
  ogl-test.h
  CMakeLists.txt
CMakeLists.txt

CMakeLists.txt:

cmake_minimum_required (VERSION 3.8)

project("ogl-renderer")

set(GLFW_BUILD_DOCS OFF CACHE BOOL "" FORCE)
set(GLFW_BUILD_TESTS OFF CACHE BOOL "" FORCE)
set(GLFW_BUILD_EXAMPLES OFF CACHE BOOL "" FORCE)

add_subdirectory ("lib/glfw-3.3.2")

add_subdirectory ("src")
add_subdirectory ("test")

enable_testing()

add_test (ogl-renderer olg-test)

src/CMakeLists.txt:

cmake_minimum_required (VERSION 3.8)

add_library (ogl-renderer "engine/renderer.cpp" "engine/renderer.h" "engine/renderer.cpp" "engine/renderer.h" "engine/Window.cpp" "engine/Window.h" "engine/Shape.cpp" "engine/Shape.h" "engine/message-queue.cpp" "engine/message-queue.h" "engine/messages/window-mgmt.h" "engine/messages/window-mgmt.cpp")

target_link_libraries(ogl-renderer glfw)

test/CMakeLists.txt:

add_executable (ogl-test "ogl-test.cpp" "ogl-test.h")

target_link_libraries(ogl-test ogl-renderer)

test/ogl-test.cpp:

#include "../src/ogl-renderer.h"

void testWindow() {
    NglRenderer::startRenderer();

    int windowId = NglRenderer::createWindow("Test", 640, 480);
}

int main() {
    testWindow();
}

Errors:

Error   LNK2019 unresolved external symbol "void __cdecl NglRenderer::startRenderer(void)" (?startRenderer@NglRenderer@@YAXXZ) referenced in function "void __cdecl testWindow(void)" (?testWindow@@YAXXZ)  C:Userschansensourcereposogl-rendereroutbuildx64-Debugogl-renderer C:Userschansensourcereposogl-rendereroutbuildx64-Debugogl-test.cpp.obj 1

Error   LNK2019 unresolved external symbol "int __cdecl NglRenderer::createWindow(char *,int,int)" (?createWindow@NglRenderer@@YAHPEADHH@Z) referenced in function "void __cdecl testWindow(void)" (?testWindow@@YAXXZ) C:Userschansensourcereposogl-rendereroutbuildx64-Debugogl-renderer C:Userschansensourcereposogl-rendereroutbuildx64-Debugogl-test.cpp.obj 1

I am able to fix it by always including the .h and .cpp files in every location, but I want to figure this out the right way. I understand that I need to compile the source project into a library, then link that to the test executable, but I can’t figure out how to do it correctly. I’m not even entirely certain how correct my CMakeList.txt files even are. I either guessed or copied on all these configurations.