Add small test for KoZoomAction

Before this commit, KoZoomAction class didn't have any tests for itself.
This commit adds a very small, easy test.
(I `just needed it to check something, it should be expanded to be a real
test, for now it checks very basic functionality).

(cherry picked from commit fe4d08407690dafac7d84b37b65dcbcb8824a0ec)