I don't understand your system so you need to draw it. Normally a single well will simply either have test connections for a mobile test separator or 3 phase meter or will connect at a manifold with other wells to a test header so that individual wells can be tested.
But there might be a different type of test. Please elaborate.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
Kind of. Oil fields typically sell oil by the lease. The allocation back to the wells (for engineering analysis) is based on periodic well tests. You shift a well to test, assign a flow rate and assume that this flow rate remains constant (or at least a constant proportion of the total field) until the next test.