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A green build does not prove that a check examined the condition it was meant to protect. The check may have skipped its work entirely, or it may have inspected only part of the input. In both cases, the process can finish successfully while a real defect goes unnoticed.
How can a check pass when the thing it checks is broken?
A check only provides evidence about the inputs it actually examines and the failures it is able to detect. If its assumptions stop matching the build output, it can still run without errors while no longer testing the intended condition.
Othmane ETTAIB describes two distinct failures in a verifier: one check skipped its comparison after a bundle filename changed; another parsed only CSS rules in one formatting style. The first inspected nothing because a guard blocked execution. The second inspected an incomplete set.
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The verifier expected a bundle at the fixed path app.js. It ran its comparison only when that bundle and a privacy page both existed. After cache-busting fingerprinting renamed the bundle to a form such as app.<hash>.js, the fixed-path existence test became false. The comparison body never ran, and the build continued with zero reported errors.
The problem was not that the comparison found the bundle correct; it never reached the comparison. A guard meant to prevent work when required files were absent had silently become a switch that disabled the check when a legitimate build-name change occurred.
Make the expected artifact explicit
ETTAIB’s fix was to find the bundle by its expected hashed filename shape and fail unless exactly one matching bundle exists. This changes a silent skip into an explicit failure when the expected artifact is missing or ambiguous. The exact matching pattern depends on the project’s naming convention; the essential requirement is that the check cannot quietly continue without the file it needs.
How formatting made a CSS check miss real rules
A second check used a regular expression to find CSS @font-face blocks. Its pattern required the opening brace immediately after @font-face, so it matched compact output like @font-face{...} but not output with a space, like @font-face {...}.
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Some generated CSS used the spaced form for real declarations, while generated fallback rules did not. As a result, the pattern saw the generated rules but missed real declarations. The comparison operated on an incomplete set and could pass despite missing fallbacks.
Allow the formatting the output actually uses
The stated fix was to permit whitespace between @font-face and the opening brace in the pattern. With that mismatch corrected, deliberately removing a fallback made the check fail as intended. This example is about a pattern’s coverage: a parser that recognizes only one serialization style can appear to validate a complete file while overlooking valid rules written another way.
How to prove a check can catch the failure it claims to catch
Give the check a known failure to detect. If it is meant to catch a missing fallback, temporarily remove one. If it depends on a generated artifact, verify that a missing or unexpected artifact causes a failure rather than a skipped comparison.
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- Identify the specific defect the check is supposed to catch.
- Introduce that defect deliberately in a controlled change or test fixture.
- Run the check and confirm it produces a failure signal.
- Restore the protected behavior and confirm the check passes again.
ETTAIB’s practical advice is to “after writing a check, break the thing it protects and watch it scream.” A check that has only been observed passing has not yet shown that it can detect the claimed failure.
What these examples do—and do not—show
The two cases illustrate different ways a successful process can be an ineffective instrument: a guard can prevent the check from running, and a parser can run while overlooking part of its input. They are examples from one verifier, not evidence about how often these problems occur across software projects. The useful diagnostic is to ask not only whether the build is green, but what inputs the check examined and whether a controlled failure makes it go red.
Best Value
The article was written by Othmane ETTAIB and originally published at Indie Core Dev, whose blog index lists it on 1 September 2026: Indie Core Dev. The verifier code is available on GitHub.
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