Fatal error if cohort_role_sync task is run when an assigned role no longer exists

Test 1: Deleting the cohort role assignment without syncing first

As admin:

1. Clone new site (mdk create -v BRANCH)
2. Checkout last week's weekly:
   • Master: git checkout 8cf4c97217230e74
   • 38: git checkout 773b1f738fa
   • 37: git checkout fcc93935bea
3. Install the site
4. Create a cohort and add some users to it, including user t1 (or any user, just remember their username)
5. Create a new role 'cohortmanager', based on manager (Admin -> Users -> Define roles) and make sure to check the "User" box next to the "Context types where this role may be assigned" option.
6. Now, via the cohorts role assign page (Admin -> Users -> Assign user roles to cohort), assign the cohortmanager role to the t1 user for that cohort.
7. Now, go back to define roles via system admin
8. Delete the 'cohort manager' role
9. Now, run the sync task:

   php admin/tool/task/cli/schedule_task.php --execute=\\tool_cohortroles\\task\\cohort_role_sync

   Verify you see a bunch of errors

10. Now, checkout HEAD (git checkout master or git checkout MOODLE_38_STABLE, etc)
11. Run the upgrade
12. Verify the upgrade runs without any errors
13. Now, run the following query (change table prefix as needed):

    select t.*, r.id from mdl_tool_cohortroles t left join mdl_role r on t.roleid = r.id where r.id is null;

    Verify there are 0 results;

14. Now, run the following query (change table prefix as needed):

    select ra.*, r.id from mdl_role_assignments ra left join mdl_role r on ra.roleid = r.id where r.id is null;

    Verify there are 0 results;

15. Now, run the sync task:

    php admin/tool/task/cli/schedule_task.php --execute=\\tool_cohortroles\\task\\cohort_role_sync

    Verify the task completes without any errors

Test 2: Deleting the cohort role assignment after syncing

1. Clone new site (mdk create -v BRANCH)
2. Checkout last week's weekly:
   • Master: git checkout 8cf4c97217230e74
   • 38: git checkout 773b1f738fa
   • 37: git checkout fcc93935bea
3. Install the site
4. Create a cohort and add some users to it, including user t1 (or any user, just remember their username)
5. Create a new role 'cohortmanager', based on manager (Admin -> Users -> Define roles) and make sure to check the "User" box next to the "Context types where this role may be assigned" option.
6. Now, via the cohorts role assign page (Admin -> Users -> Assign user roles to cohort), assign the cohortmanager role to the t1 user for that cohort.
7. Now, run the sync task:

   php admin/tool/task/cli/schedule_task.php --execute=\\tool_cohortroles\\task\\cohort_role_sync

8. Delete the 'cohort manager' role
9. Now, run the sync task:

   php admin/tool/task/cli/schedule_task.php --execute=\\tool_cohortroles\\task\\cohort_role_sync

   You may see some errors. If so, that's ok.

10. Now, checkout HEAD (git checkout master or git checkout MOODLE_38_STABLE, etc)
11. Run the upgrade
12. Verify the upgrade runs without any errors
13. Now, run the following query (change table prefix as needed):

    select t.*, r.id from mdl_tool_cohortroles t left join mdl_role r on t.roleid = r.id where r.id is null;

    Verify there are 0 results;

14. Now, run the following query (change table prefix as needed):

    select ra.*, r.id from mdl_role_assignments ra left join mdl_role r on ra.roleid = r.id where r.id is null;

    Verify there are 0 results;

15. Now, run the sync task:

    php admin/tool/task/cli/schedule_task.php --execute=\\tool_cohortroles\\task\\cohort_role_sync

    Verify the task completes without any errors