Tests that cannot be automatized should occasionally be run manually.
Unused code, in particular unused functions, can be detected with the tool xunused.
cd build
cmake .. -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
vi compile_commands.json # rm source files in 3rdparty and Fit/3rdparty
xunused compile_commands.json 2>&1 >/dev/null | tee /io/unused.txt
Use judgement: not all currently unused functions must be removed.
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