What is the test for determining who gets priority right to pay a debtor in an action?

Hallett J.A. starts with the seminal case of Dearle v. Hall (1823), 3 Russ. 1; 38 E.R. 475, where it was held that the assignee of a chose in action who first notified the party legally obliged to pay the assignor, of the assignment, had priority right to payment, over the assignee whose assignment pre-dated that of the notifying assignee but who failed to give notice to the debtor before the subsequent assignee gave notice. This equity deviation, from what Hallett J.A. describes as “fundamental logic and law that if a person effectively transfers all of his or her interest in property to another there is nothing left to subsequently transfer to a third party”, is justified because of the necessity to avoid fraudulent subsequent transfers. As Hallett J.A. says, “equity alters the logic to protect innocent third parties without notice of the true state of the title to the property who may be persuaded to acquire such property for valuable consideration or lend money on the security of the same”.