ConcatWorker constructed ConcatEngine in place while ConversionWorker reached its engines
through ConversionDependencies. That asymmetry is the whole reason one worker had a tested
failure path and the other had none: everything past setForeground was untested on *every*
source set, JVM and device alike.
The repo had already measured the cost and written it down. PerJobStagingTest's KDoc
records that **reverting ConcatWorker to a constant staging name left all 257 tests
green**, because nothing could reach the line that names the file. RefusedJobTest says it
from the other side -- "the next thing past the count guard is ConcatEngine, which is
native". That mutation is red now.
The seam is `ConversionDependencies.concat: (Context) -> ConcatJoiner`, beside .hardware
and .software. ConcatEngine implements the interface; its Result type stays nested in the
implementation, because moving it would touch every call site to buy nothing -- what a
test needs is the ability to not run FFmpeg, and that is the method, not the type.
Five tests, and the mutations that hold them:
the engine's own reason reaches the user replace e.message with the generic string
a failure with no message still says one drop the ?: GENERIC_FAILURE_MESSAGE fallback
a failed join deletes its partial drop staged.delete() from the catch
no input array at all is refused swap in TOO_FEW_INPUTS_MESSAGE
a join reports its own staged file revert to the constant staging name
The delete test was vacuous on its first draft and the mutation caught it: it scanned the
staging directory for a "join-" prefix that StagingNames.forJob does not produce -- it
names files <jobId>.<ext> -- so the assertion was trivially true. Rewritten to assert
against the handle the joiner was actually given.
Two small fixes ride along, both the repo's own conventions rather than new opinions.
"No input files." becomes NO_INPUTS_MESSAGE, per #158: a message the user can see is
named once, so a test asserts the string the worker writes rather than a copy that can
drift. And the JVM now covers that arm, which ran before staging and before any native
code and had no business being a device test.
579 -> 584 JVM tests, 0 failures.
ConcatWorker: 14 -> 5 missed lines, 2 -> 0 missed branches.
Line 2173/2348 -> 2183/2352; branch 1091/1342 unchanged in the numerator.
The line denominator moved 2348 -> 2352: that is the ConcatJoiner interface, not new
untested code. Said plainly because CLAUDE.md's coverage entry has a history of explaining
its own numbers wrongly.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
JMR-devandClaude Opus 5
aa7e1d8b01