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# addTestObserver(_:)

Registers an object conforming to [`XCTestObservation`](/documentation/XCTest/XCTestObservation) as an observer for the current test session.

```
func addTestObserver(_ testObserver: any XCTestObservation)
```

## Discussion

Observers may be added at any time, but will not receive events that occurred before they were registered. The observation center maintains a strong reference to observers.Events may be delivered to observers in any order. Given observers A and B, A may be notified of a test failure before or after B. Any ordering dependencies or serialization requirements must be managed by clients.

---

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