Case context: A team selected a test set but cannot say whether it gives high confidence in the system's overall performance. They argue that choosing any test-set size completes the task.

Question: Diagnose the team's mistake and state what it should require before treating the test set as sufficiently large.

Sample answer: The team has not applied the source's criterion. Merely choosing a size is insufficient; the test set should be large enough to give high confidence in the system's overall performance.

Key points:

• Choosing any size does not establish adequacy.
• Adequacy requires high confidence.
• Confidence must concern overall system performance.
• The test set should be large enough to meet that requirement.

Rubric: The response should identify the missing high-confidence requirement and connect it explicitly to overall system performance and adequate test-set size.