Mutation testing found the decision rule was effectively untested. Four defects
injected into it - removing the silence guard, comparing shifts instead of
tones, never setting the hysteresis anchor, and inverting the comparison - all
left the entire suite green. The rule lived inside CwDeepDecoder, which needs an
Android Context and a loaded ONNX session, so tests could only restate it, and a
restated rule cannot fail when the real one is wrong.
CwShiftDecider now holds the rule as a pure class that both the decoder and the
tests drive. Its outcome is reported as an enum so the decoder's logging is a
presentation concern rather than a second copy of the logic. CwShiftDeciderTest
targets each of the four surviving mutants directly.
MIN_PROMINENCE lowered from 8.0 to 4.5. Raising it to 8.0 last round overshot:
measured on 400 ms windows of keyed CW in noise, a comfortably copyable signal
reaches only 7.6-9.0 at 0 dB SNR and 5.2-6.7 at -3 dB, so 8.0 silently refused
to shift weak out-of-window signals - the exact failure the feature exists to
prevent. Pure noise peaks at 2.2-3.4, so 4.5 keeps zero false positives across
40 noise windows while retaining the weak end. A false tone is worse than a
missed one: it moves a good signal out of range, whereas a miss leaves the audio
alone until a stronger window arrives. Windows dominated by keying gaps measure
2.4 and are indistinguishable from noise at any threshold; those are skipped.
Test files reorganised to match: the decision rule is covered by
CwShiftDeciderTest against real code, signal-level properties by
CwToneShiftSignalTest, and the restated-logic file it replaces is gone.
80 CW tests pass, golden vectors included.
mckero
ea125d7db4