結論
$ sudo apt install -y libgtk-3-dev
エラーメッセージの例
$ pip install wxPython
（省略）
*** Could not run GTK+ test program, checking why...
*** The test program failed to compile or link. See the file config.log for the
*** exact error that occurred. This usually means GTK+ is incorrectly installed.
configure: error:
The development files for GTK+ were not found. For GTK+ 2, please
ensure that pkg-config is in the path and that gtk+-2.0.pc is
installed. For GTK+ 1.2 please check that gtk-config is in the path,
and that the version is 1.2.3 or above. Also check that the
libraries returned by 'pkg-config gtk+-2.0 --libs' or 'gtk-config
--libs' are in the LD_LIBRARY_PATH or equivalent.
（省略）
補足
wxPython のインストールはめちゃくちゃに時間がかかります*1。
*1:スペックにもよりますが 1時間～12時間
