What are the enrollment dates of all the tests that have result "Pass"?
SELECT T1.date_of_enrolment FROM Student_Course_Enrolment AS T1 JOIN Student_Tests_Taken AS T2 ON T1.registration_id   =   T2.registration_id WHERE T2.test_result   =   "Pass"
enrollment dates refers to date_of_enrolment; tests that have result \"Pass\" is represented by test_result = \"Pass\"; joining tables on registration_id to match student course enrolments with their test results.