Actually, I looks like the test-suite used by Debian is deprecated [0]. I've prepared another patch for Ubuntu [1], which instead imports upstream's current test-suite to debian/tests/ and makes use of it.
For some reason upstream's test/ and tests/ directories (the current test-suite) are missing in Debian's orig.tar.gz archive... Maybe this can be fixed with the next version bump? Best, Lukas [0] https://github.com/httplib2/httplib2/issues/166 [1] https://paste.ubuntu.com/p/T2vBYYjgpG/