How many students passed the test?
SELECT count ( T1.student_id )  FROM Student_Course_Enrolment AS T1 JOIN Student_Tests_Taken AS T2 ON T1.registration_id   =   T2.registration_id WHERE T2.test_result   =   "Pass"
students passed the test refers to WHERE test_result = 'Pass'; count of students refers to COUNT(student_id);