The teacher did not take the test today as all the students were not present

[kstrch]

'The teacher did not take the test today
as all the students were not present.'
What is wrong in this sentence?
I understand that it must be related to the tense.
Two incidents are happening here, 1st one is students' absence and second one is the teacher's not taking the test.
As the first one happened earlier, that is all were not present this thing has happened a bit earlier than the second one. after watching their absence teacher didnot take the test. So it can be written as: 'Teacher didnot take the test today as all the students had not been present.' or, 'Teacher hasnot taken the test today as all the students werenot present.'
Is that what is wrong in that sentence? or there is something else. Please help

[Alan]

---> as NOT ALL (of) The students were present.