A gap audit over the eight branches merged together looked for lines still
never executed and asked, for each, whether something already accounts for it.
Everything mapped except one: `ConcatWorker.kt:42`, the refusal of a join with
fewer than two inputs.
Its neighbour maps. `ConcatWorker.kt:40` -- the missing-URI-array arm, two lines
above -- is covered on the device by
`UnopenableUriTest.aJoinWithNoInputArrayFailsWithAMessage`. That is invisible to
JaCoCo, which measures `testDebugUnitTest` only, so the report shows both arms
cold and cannot distinguish the one that is e2e-covered from the one nothing
touches. Only reading the androidTest source separates them.
`grep` says nothing in either source set mentions "Pick at least two files to
join." Two tests here now do:
- `a join of a single file is refused with a message rather than joined` pins
the verdict and the message together, via `Failure.equals`, for the reason the
file's header already gives.
- `a join of two files is not refused for its count` is the control that puts
the assertion on the boundary rather than on the string. It refuses the
*space* rather than letting the job run: the next thing past the count guard
is `ConcatEngine`, which is native, and `NamingPublisher`'s KDoc already
records that no JVM test gets past it. A failure carrying the space message is
proof execution reached line 57, which is proof it cleared line 42, at no
engine cost.
Reachability is the header's argument plus one of its own: `request(...)` takes
a `List<Uri>` and checks nothing about its length, so a one-item join is a
well-formed call rather than a corrupted queue entry.
Mutations, each killing exactly the test it should:
| mutation | red |
|---|---|
| guard deleted outright | `a join of a single file is refused...` |
| `uris.size < 2` -> `< 3` | `a join of two files is not refused for its count` |
Restored, both green. Gate green: assembleDebug, testDebugUnitTest,
compileDebugAndroidTestKotlin, ktlintCheck, detekt, lintDebug.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
JMR-devandClaude Opus 5
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