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A green build check does not prove that it inspected the right files or even ran its verification logic. In one verifier, a renamed JavaScript bundle made an existence guard skip the check entirely; in another, a CSS regular expression missed rules whose formatting differed by one space. Both checks passed while the behavior they were meant to protect was broken.
How can a check pass when the protected behavior is broken?
A check can report success without detecting a problem if it skips its work or examines only part of its input. The result says the process completed without reporting an error; it does not, by itself, establish that the check saw the condition it was designed to catch.
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Othmane ETTAIB describes two different failure mechanisms in a verifier: a guard clause that stopped the verification code from running, and a regular expression that parsed only some of the generated CSS. The distinction matters: one check inspected nothing, while the other inspected an incomplete set.
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The verifier looked for a JavaScript bundle at a fixed path, app.js, and performed its comparison only when that bundle and a privacy page both existed. Once cache-busting fingerprinting changed the bundle name to a form such as app.<hash>.js, the fixed-path existence test returned false. The comparison was skipped, and the build continued with zero reported errors.
There was no explicit failure for the missing expected artifact. A condition intended to prevent invalid comparisons had become an off switch: the check’s success path included doing no check at all.
Make the expected input explicit
The described fix was to locate the bundle by its expected hashed filename shape, then fail unless exactly one matching bundle exists. That makes an absent or ambiguous artifact an error instead of a reason to skip verification. The verifier code is available on GitHub.
When a pattern checks only part of the output
A second check compared CSS @font-face rules to detect missing fallback declarations. Its regular expression expected the opening brace immediately after @font-face, so it matched compact output such as @font-face{...} but missed output formatted with a space, @font-face {...}.
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How to tell whether a check can catch its claimed failure
Give the check a controlled failure to detect. Break the behavior it claims to protect, run the check, confirm that it produces a failure signal, and then restore the behavior. ETTAIB sums up the habit this way: “after writing a check, break the thing it protects and watch it scream.”
A check that has only been observed passing has not yet demonstrated that it can catch the failure it claims to catch. The deliberate break tests the connection between the protected behavior and the check’s failure signal—not just whether the check command runs.
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What these examples do—and do not—show
These are two examples from one verifier, not evidence that either failure is common across software checks generally. They illustrate a useful diagnostic question: did the check inspect the intended input, and would a relevant fault make it fail? A successful run answers neither question unless the check’s inputs and failure behavior are verified.
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