"undefined reference to" errors in my cmake project - c++

Question

I'm having a bit of trouble organizing my c++ project as a cmake project, which is something I'm new to. I'm trying to mimic the template given by this github repository. I think I'm almost there, but I'm getting a few linker errors when I try to compile with the following commands:
cd markets
rm -rf build/manual
mkdir build/manual
cd build/manual
cmake -G "Unix Makefiles" -D CMAKE_CXX_COMPILER=/usr/bin/g++-8 ../..
make
There's a lot of output, but here are the first few lines:
[100%] Linking CXX executable markets_tests
CMakeFiles/markets_tests.dir/src/test_data_handler.cpp.o: In function `Testtest_data_handler::RunImpl() const':
test_data_handler.cpp:(.text+0x12a): undefined reference to `Instrument::Instrument(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
test_data_handler.cpp:(.text+0x153): undefined reference to `Instrument::Instrument(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&)'
test_data_handler.cpp:(.text+0x37f): undefined reference to `DataHandler::DataHandler(std::vector<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::allocator<std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > > > const&, unsigned int const&, unsigned int const&)'
CMakeFiles/markets_tests.dir/src/test_data_reader.cpp.o: In function `Testtest_csv_reader::RunImpl() const':
test_data_reader.cpp:(.text+0xa9): undefined reference to `csv_reader(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >, unsigned int)'
I guess this must mean that something is wrong with my markets/test/CMakeLists.txt file, which I have now as:
cmake_minimum_required(VERSION 3.10)
project(markets_tests)
find_package(UnitTest++ REQUIRED)
find_package(Eigen3 3.3 REQUIRED NO_MODULE)
SET(GCC_COVERAGE_COMPILE_FLAGS "-no-pie")
SET(CMAKE_CXX_FLAGS "${GCC_COVERAGE_COMPILE_FLAGS}")
include_directories(${MARKETS_HEADERS_DIR})
include_directories(${UTPP_INCLUDE_DIRS})
set(SOURCE_FILES main.cpp
src/test_data_handler.cpp
src/test_data_reader.cpp
src/test_exec_handler.cpp
src/test_fill.cpp
src/test_instrument.cpp
src/test_market_bar.cpp
src/test_market_snapshot.cpp
src/test_order.cpp
src/test_pnl_calculator.cpp
src/test_portfolio.cpp
src/test_position_summary.cpp)
add_executable(markets_tests ${SOURCE_FILES})
target_link_libraries(markets_tests markets Eigen3::Eigen UnitTest++) # added Eigen
install(TARGETS markets_tests DESTINATION bin)
Any ideas? Other questions seem to suggest that I could be linking things in the wrong order, but this project structure isn't that complicated (just an executable, a library, and some unit tests). This was compiling with my old makefile, so I doubt it's because I haven't defined some of the header definitions.
Here is the tree of my markets/ root directory if it helps:
.
├── bin
├── build
│   └── manual
├── CMakeLists.txt
├── docs
├── lib
├── README.md
├── src
│   ├── CMakeLists.txt
│   ├── main.cpp
│   └── markets
│   ├── CMakeLists.txt
│   ├── data_handlers.cpp
│   ├── data_handlers.h
│   ├── data_readers.cpp
│   ├── data_readers.h
│   ├── execution_handler.cpp
│   ├── execution_handler.h
│   ├── fill.cpp
│   ├── fill.h
│   ├── instrument.cpp
│   ├── instrument.h
│   ├── market_bar.cpp
│   ├── market_bar.h
│   ├── market_snapshot.cpp
│   ├── market_snapshot.h
│   ├── order.cpp
│   ├── order.h
│   ├── pnl_calculator.cpp
│   ├── pnl_calculator.h
│   ├── portfolio.cpp
│   ├── portfolio.h
│   ├── position_summary.cpp
│   └── position_summary.h
└── test
├── CMakeLists.txt
├── main.cpp
├── src
│   ├── test_data_handler.cpp
│   ├── test_data_reader.cpp
│   ├── test_exec_handler.cpp
│   ├── test_fill.cpp
│   ├── test_instrument.cpp
│   ├── test_market_bar.cpp
│   ├── test_market_snapshot.cpp
│   ├── test_order.cpp
│   ├── test_pnl_calculator.cpp
│   ├── test_portfolio.cpp
│   └── test_position_summary.cpp
└── test_data
├── QLD.csv
└── SPY.csv
Edit:
Here is src/markets/CMakeLists.txt
cmake_minimum_required(VERSION 3.10)
project(markets)### C CXX)
set(SOURCE_FILES
data_handlers.h
data_handlers.cpp
data_readers.h
data_readers.cpp
execution_handler.h
execution_handler.cpp
fill.h
fill.cpp
instrument.h
instrument.cpp
market_bar.h
market_bar.cpp
market_snapshot.h
market_snapshot.cpp
order.h
order.cpp
pnl_calculator.h
pnl_calculator.cpp
portfolio.h
portfolio.cpp
position_summary.h
position_summary.cpp
)
find_package (Eigen3 3.3 REQUIRED NO_MODULE)
add_library(markets SHARED STATIC ${SOURCE_FILES})
target_link_libraries(markets Eigen3::Eigen stdc++fs) #added this
install(TARGETS markets DESTINATION ${MARKETS_INSTALL_LIB_DIR})
install(FILES markets.h DESTINATION ${MARKETS_INSTALL_INCLUDE_DIR})