CLONE - A teacher can prevent students from accessing an activity between specified dates

This test requires conditional availability to be enabled by an administrator in Site administration > Advanced features.

1. Login as a teacher, access an activity and edit the settings.
2. Tick the checkbox to enable an accessible from date and set a date in the future.
3. Select 'Show activity greyed-out, with restriction information' for 'Before activity is available'.
4. Login as a student, view the course page and check that the activity is shown greyed-out with the accessible from date specified.
5. Login as the teacher again, access a different activity and edit the settings.
6. Tick the checkbox to enable an accessible until date and set a date in the past.
7. Select 'Hide activity entirely' for 'Before activity is available'.
8. Login as a student, view the course page and check that the activity does not appear.