Teachers have to report a teacher assessment at the end of year 2 in each subject. If a child is working at level 2 or above, they have to complete just one test in each subject (reading, writing and maths) to form part of the vast evidence for this assessment.
The test can be used at any stage in the year - a teacher could use a test in September to confirm where a child is at that point, then use teacher assessment for the rest of the year to prove a child's progress moving on from that result.
Most Y2 teachers prefer to do the tests at this time of year to help confirm their near final assessment.
A child should not sit a level 2 test and then go on to complete a level 3 test also - this is poor teacher assessment, and makes the child jump through unnecessary hoops - if a child is level 3, the teacher assessment should already show that.
Most Y2 teachers administer the tests as part of 'normal' lessons, in groups, so that children are not even aware they are doing them. They are only 6 and 7 years old, fgs!
Makes me sad to hear on teachers enforcing more than one test in each subject on children, or even worse taking them into the hall to sit them, as one thread reported on here. Completely unnecessary and mean.