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Custom exception
Learn Custom exception in Apex with a construct-specific explanation, a unique example, a practical boundary, and a mastery check.
Custom exception is an atomic Apex topic inside Testing & Integration. The example below uses the actual construct named by the lesson rather than a generic placeholder.
Focus on what Custom exception changes: the input, binding, control path, object state, collection, runtime effect, or language contract. Then alter one value and verify that the behavior changes for a reason specific to this feature.
Topic-specific example
public class InvalidOrderException extends Exception {}
throw new InvalidOrderException('bad order');
Exercise both the success path and the failure path; verify what is caught, propagated, or cleaned up rather than only checking printed output.