ResearchInforme de banco de pruebas
Four models, the same real defect, a judge none of them saw
Question: Does a green suite written by the implementer prove the defect is fixed?
Its own suiteIndependent probeBaseline 5/7
Gemini 3.6 Flash (High)
187/187
6/7
Gemini 3.1 Pro (Low)
187/187
5/7
Claude Opus 4.6 (Thinking)
190/190
5/7
Claude Sonnet 4.6 (Thinking)
191/191
5/7
View the table
| Model | Its own suite | Independent probe |
|---|---|---|
| Baseline | — | 5/7 |
| Gemini 3.6 Flash (High) | 187/187 | 6/7 |
| Gemini 3.1 Pro (Low) | 187/187 | 5/7 |
| Claude Opus 4.6 (Thinking) | 190/190 | 5/7 |
| Claude Sonnet 4.6 (Thinking) | 191/191 | 5/7 |
Findings
- Four models were given the same real defect, the same prompt, and the same base, each in an isolated workspace. All four delivered clean strict typecheck, between 187 and 191 passing tests, zero forbidden patterns, and zero out-of-scope files. By any automated criterion, impeccable work.
- A probe written by the Director, unseen by any model, evaluated the result against the reproduction of the defect. The baseline passed 5 of 7 cases. Three of the four models still passed 5 of 7: the defect was untouched. One reached 6.
- Each model added its own passing tests. Those tests encode its own understanding of the defect, and when that understanding is wrong, the green test certifies the misunderstanding instead of catching it.
- The most instructive case diagnosed the defect precisely in a code comment, wrote the fix, added tests, and the defect still got through. Understanding a failure and solving it are two different capabilities, and this experiment separates them for the first time.
- The only one that improved came from a different family than the two that failed identically. With a single provider there would have been no improvement at all.
- Time did not predict quality: the slowest and the fastest scored the same, and the winner sat in between.
What this does NOT say
- n = 1 per model. One task, one run. It is not a measure of general capability.
- A single class of defect, which may favor some models over others.
- It does not measure cost or tokens: the tool does not expose them in non-interactive mode. A measured limitation, not an omission.
- One model was excluded with evidence: its quota was exhausted and the tool silently substituted another. Including it would have measured the same engine twice.