From commit 880896c6f4814f4c7798355a652dc6167be2b75f in googletest cmake
test configuration fails with errors like
CMake Error: install(EXPORT "gtestConfigInternal" ...) includes target
"gtest" which requires target "i3ipc++" that is not in the export set.
The issue was that link_libraries also affected the googletest internal
targets that came after it making the whole thing fail.
This could also have been solved by moving link_libraries after the
configuration of googletest but according to the cmake documentation [1]
target_link_libraries should be prefered over link_libraries anyways.
[1]: https://cmake.org/cmake/help/latest/command/link_libraries.htmlFixes#1393
googletest (gtest) is more feature rich than the current implementation
which only provides expect() which is basically an assertion. It is also
quite intuitive to use, this can be seen in the rewrite of the
command_line test where EXPECT_THROW replaces a whole try-catch block.
I have also moved the source files the test depend on to be linked in
CMakeLists.txt instead of including them directly because include .cpp
files is bad.
The two x11 tests were removed because they were written two years ago
and a lot of the things they depend on, don't actually exist anymore in
polybar (I think we switched to xpp after those tests were written)
Tests are now compiled with the gcov lib which can be used to provide
test coverage in a second step
