This is part 1 that does the back-end:
1. New table role_allow_switch.
2. Upgrade that copies all the allows from role_allow_assign, and then drops the old CFG->allowuserswitchrolestheycantassign.
3. Old function get_assignable_roles_for_switchrole renamed to get_switchable_roles and changed to use the new table. Fixes MDL-18604 in HEAD.
4. Switch callers to use the new function name.
5. Unit tests for this new function.
6. To make those unit tests work, new switch_global_user_id and revert_global_user_id methods in UnitTestCaseUsingDatabase for toggling $USER->id.
I still need to do the editing interface under Administration ► Users ► Permissions ► Define roles. That will be done as a second commit.
This is not as ambitious as the abortive FakeDBUnitTests scheme, but this one works for simple cases.
There is a new test case class UnitTestCaseUsingDatabase to inherit from. I hope it is sufficiently well documented in its PHPdocs.
* It users $CFG->unittestprefix.
* You can access that database using $this->testdb.
* That database is empty by default, you have to call create_test_table to create the ones you want, and drop_test_table to clean them up in the end. The table definitions are read from the XMLDB file.
* When you are ready to call real Moodle code that users $DB, call switch_to_test_db and then revert_to_real_db when you are done.
* If you forget to call drop_test_table or switch_to_test_db, the class will attempt to clean up after you, but will also print rude developer debug messages telling you not to be stupid.
* There is also a load_test_data method for populating a table from an array.
The is an example of its use in lib/simpletest/testunittestusingdb.php.
