If your final test is effectively worth 10 marks (being counted double) and you score 0 on it, you will have 37.1 / 50.0 in Tests category. This would bring your final mark down to 85.75% - which would give you a grade A only if it gets rounded up to the nearest whole number.
To be sure, you would need to score at least 0.15 / 5 (counting as 0.3 out of 10 and giving you 37.4 / 50.0). This would give you a final mark of 86.05%.
But you need to be careful. Some grading systems operate on a 'minimum threshold' basis, whereby you need to score a minimum of a certain minimum mark in each test. So - go for the highest mark you can!