Given github.com/chewing/libchewing@69ae0e454a/CMakeLists.txt (L167-L169) it's better not build testhelper when tests are disabled.
Given https://github.com/chewing/libchewing/blob/69ae0e454a34c9ac193fc648a7215f06b5e9c52a/CMakeLists.txt#L167-L169 it's better not build testhelper when tests are disabled.