Over-Mocking Is a Governance Problem, Not a Review Smell

The 2026 empirical study of 1.2 million commits and 48,563 coding-agent commits (arxiv 2602.00409, Hora and Robbes, MSR 2026) found agent test commits add mocks 36% of the time versus 26% for non-agent commits, agents concentrate on a single test-double type, and the resulting suites are more brittle than the human baseline. The precedent is load-bearing; the smell reproduces at generation speed; per-PR review catches at reading speed. The corrective move lives at the convention layer, not in the review pass.