Add unit tests

The module has no unit tests, yet. Add some that cover the core cases:

• Anonymous user goes to home page, gets redirected to (mock) SSO, then to configured landing page.
• Anonymous user goes to interior page, after returning from (mock) SSO, is redirected to original destination.
• Logged in user goes to an allowed page, gets the page
• Logged in user goes to an unallowed page, gets an access denied error