CollectionScheduler: add tests for the actual QTimer interval
Summary:
Testing the data structures is all fine and good, but I wanted to
make sure the actual underlying timer was set to the right interval,
after all that std::chrono wrangling.
Test Plan: collectionschedulertest still passes
Reviewers: dvratil
Reviewed By: dvratil
Subscribers: kde-pim
Differential Revision: https://phabricator.kde.org/D20483