The code uses Lock() instead of RLock() for a read-only operation. This method only reads totalTests, totalTestPassed, and totalTestFailed without modifying them. It should use RLock() to allow concurrent reads, which would improve performance and is more semantically correct.

The instance-level mutex stateMu is being used to protect package-level global variables (completeTestReport, failedTCsBySetID, totalTests, etc. defined at lines 40-50). If multiple Replayer instances run concurrently (e.g., in different goroutines or if multiple instances are created), each instance would have its own mutex but they would all access the same global variables, making the synchronization ineffective. The mutex should either be global (package-level) or the protected state should be moved to instance-level fields within the Replayer struct.

The code uses Lock() instead of RLock() for read-only operations. Since this code only reads the shared state variables (totalTests, totalTestPassed, totalTestFailed) and creates snapshots, it should use RLock() to allow concurrent reads, which would improve performance. Using Lock() here unnecessarily blocks other readers.

The code uses Lock() instead of RLock() for read-only operations. Since this code only reads the shared state variables to create snapshots without modifying them, it should use RLock() to allow concurrent reads and improve performance.

The snapshot creation for failedTCsBySetIDSnapshot uses a shallow copy of the slice values. If the slices in failedTCsBySetID are modified after this snapshot is created, it could lead to race conditions or unexpected behavior. Consider using deep copy: failedTCsBySetIDSnapshot[key] = append([]string(nil), val...)

i think the solution is
Create a failedTCsBySetIDSnapshot inside the RLock() section
use deep copt for the slice
failedTCsBySetIDSnapshot := make(map[string][]string, len(failedTCsBySetID))
for key, val := range failedTCsBySetID {
failedTCsBySetIDSnapshot[key] = append([]string(nil), val...)
}

Good point! updated the snapshot to deep-copy the slice values.

The code uses Lock() instead of RLock() for a read-only operation. This method only reads from completeTestReport to create a snapshot and doesn't modify the shared state. It should use RLock() to allow concurrent reads, which would improve performance and is more semantically correct for read-only operations.