Rule tested on one path only

What goes wrong

The same rule is reachable through several equivalent entry points or duplicated call paths, and the new tests enter just one of them. The siblings keep no assertion of their own. The reader relies on a passing suite as evidence that the rule holds everywhere it appears, when only a single site is actually pinned.

Example

A newly added settle wait is asserted only where the wrap-up path invokes it; the main pass can drop the wait entirely and the suite still reports green.

Not to be confused with

Not Helpers Tested, Entry Point Untested: the untested site is a peer path of equal standing, not a surface layered above the helper that was covered.

Discovered by

@sks24git GitHub

Field notes · 12

@sks24git2026-11-06

A card built every link from a trusted id, and the tests pinned that rule for two of its three links. A change that drew the third link from server text kept every test green.

Pin a safety rule on every path it covers. A test on two of three paths lets the third drift.
Feed the hostile value in the fixture. A test without it cannot fail.

@sks24git2026-11-05

A UI copy pass replaced prototype metaphors across three screens, but only two of the three test suites asserted on the updated legend text. A regression on the third screen stays green.

Assert every rewritten user-facing string in its page test. A copy change across multiple screens needs one assertion per screen so none can silently revert.

@sks24git2026-11-04beat 1 review round

A change set out to test every best-effort write that must not fail a request, and covered three of the four. The fourth could start throwing and turn a missed hint write into an error page with every test still green.

List the whole row before testing one of it. Grep every catch of the same kind first.
Count the members, not the ones named in the ticket. The list you were handed is rarely complete.

@sks24git2026-11-04

A timing test was swapped for an output check, but the new input reaches only one of several patterns. Point any other pattern back at the full input and the slow scan returns, every test green.

Probe every reader of a capped input. A cap checked through one pattern guards only that one.
Replace a timing test with equal coverage. A narrower output check drops the rest.

@sks24git2026-10-25

A test module swapped explicit imports for a glob collector; a class nobody had ever imported woke up without the skip guard its siblings carry. Runs without the optional database now fail two tests instead of skipping.

A new collector runs what was never run. List every class it picks up and check each guard.
Count tests with and without the optional backend. A gain seen only with it hides a red run.

@sks24git2026-10-16

A chart test checked the height of one stacked band out of seven. Draw every band from that one series and the chart shows a single shape, yet the test stays green.

Assert every series, not one. A check on one band lets the others copy it unseen.
Aim one mutant at the checked value. A mutant that misses it hides the gap.

@sks24git2026-10-15beat 1 review round

A command gained a required option, and one old test still called it the old way. The new rule refuses that call, so the old test fails and the build stays red.

Grep every caller when you tighten a contract. Tests and scripts are callers too, and they break first.

@sks24git2026-09-10beat 2 review rounds

One read path was fixed to distinguish the billed amount from its foreign equivalent, and its sibling list endpoint kept the fixture where both are equal. The same substitution survives there untouched.

Apply a fixture fix to every reader of the same pair. The neighbour you skip inherits the whole defect class.

@sks24git2026-09-10beat 1 review round

The change's whole point was that two hosts police each other, yet every disabling fixture in the self-test aimed at one of them. Disable the second host and the self-test stays green.

Mirror every fixture across both sides of a mutual guarantee. One-sided coverage proves half a property and reads as all of it.

@sks24git2026-09-10beat 2 review rounds

Two methods on a widely implemented interface gained parameters, and a test double in a distant module still overrode the old shape. Nothing local failed; the break appeared only when that module compiled.

Compile every module that implements the interface you changed, not the one you edited.
A green local build is a statement about your module alone.

@sks24git2026-09-07beat 4 review rounds

Every test of a new wait entered through the second of two call paths, and tests were type-checked apart from the runner. The first path could drop the wait and the suite stayed green while type-check was red.

Run the same typecheck the gate runs. A green test runner proves nothing about types.
Pin every call path of new behaviour. One entry point tested is the other one untested.

@sks24git2026-09-07beat 2 review rounds

One knob paced two loops: a stubbed sleep in the loop under test and a real timer in the probe loop next to it. A test that set the knob to ten seconds slept ten real seconds per refused probe.

Know every consumer of a knob before a test turns it up. A stub covers one loop; the timer next to it is real.