Media3Muxers' KDoc names the defect this guards -- "the router claimed five containers
while the engine silently wrote MP4 for all of them" -- and the repair itself was
untested: Media3Engine$buildTransformer$3, the requireNotNull message lambda, was four
lines and four branches at 0%. Nothing had ever driven a plan whose container Media3
cannot mux, and factoryFor answers null for fourteen of them.
Weakening it does not crash. The wrong output is a playable file with the wrong
container, which is why a test rather than a bug report is what would catch it.
Same harness and the same two disciplines as Media3EngineEmptyCompositionTest, which is
the sibling this joins: assert the plan really is the one the test needs before driving
the engine, and rule out CancellationException so an unresumed continuation cannot read
as a pass. Three premises are asserted here rather than assumed -- that the plan is still
WebM by the time the engine sees it, that Media3 really has no muxer for WebM, and that
neither track was dropped, since the empty-composition refusal fires earlier and is a
different test's subject.
The assertion is on the exception type *and* its message, and the ticket predicted why:
replacing requireNotNull with `?: DefaultMuxer.Factory()` does not make the export
succeed, it lets it run on and fail some other way. Measured -- that mutation fails the
type assertion, so the guard is genuinely what this test is holding, and the message
assertion stands behind it.
560 -> 561 JVM tests, 0 failures. No production code changed.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
JMR-devandClaude Opus 5
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