Implement one-trigger-per-object Apex pattern with a trigger handler framework to centralize logic and enable testability

In-depth guide

Steps

1. Create a single Apex trigger per SObject (e.g., AccountTrigger.trigger) that delegates to a handler class via TriggerHandler.run()
2. Build a TriggerHandler base class that exposes virtual methods for each trigger context: beforeInsert, afterInsert, beforeUpdate, afterUpdate, beforeDelete, afterDelete, afterUndelete
3. Create a concrete handler class (e.g., AccountTriggerHandler extends TriggerHandler) overriding only the contexts you need, keeping logic out of the trigger file itself
4. Pass Trigger.new, Trigger.oldMap, and other context variables into the handler as constructor parameters so the handler is testable without real trigger execution
5. Write unit tests that instantiate the handler directly with mock data collections, bypassing the trigger to test logic in isolation
6. Use a static boolean flag in the handler to allow test methods to bypass certain side effects when needed