[ticket/281] Run calendar tests and extend calendar testing

B3P-281
[ticket/281] Fix date_to_time tests

B3P-281
[ticket/281] Fix incorrect check in calendar tests

B3P-281
[ticket/281] Add a few more tests for functions.php

B3P-281
Merge pull request #282 from marc1706/ticket/281

[ticket/281] Run calendar tests and extend calendar testing