Function check_capability_honesty 

pub fn check_capability_honesty<E, D>(
    enc: E,
    dec: D,
    img: &TestImage,
) -> Conformance
where
    E: EncoderConfig,
    D: DecoderConfig,
    <E::Job as EncodeJob>::Enc: Encoder<Error = E::Error>,
    <E::Job as EncodeJob>::AnimationFrameEnc: AnimationFrameEncoder,

Declared capabilities match real behavior.

For the encode paths (push_rows, encode_from, animation), the decode paths (streaming, animation), the lossless knob, and cheap_probe, both directions are checked: every declared capability is exercised, and every undeclared optional path must decline with UnsupportedOperation — a codec can’t claim a feature it lacks or hide one it has. The metadata channels (icc/exif/xmp/cicp) are checked bidirectionally where the decoder can observe them: each channel is supplied separately, and a declared channel must survive a PreserveExact round trip, and an undeclared one must not (a hidden write capability); the encoder-writes-but-decoder-doesn’t-read quadrant isn’t observable through decode. Separate probes allow formats with mutually exclusive ICC/native-color carriers; mixed-carrier precedence remains covered by check_color_authority_spec. native_alpha is forward-only — a declared RGBA8 round trip must preserve alpha; the no-alpha direction isn’t cleanly assertable (a codec may legitimately reject or flatten RGBA input).

All violations are collected and reported together, so one run names every dishonest flag.

Not covered: cooperative cancellation (stop) — whether a codec honors a triggered token is timing-dependent on small inputs and can’t be asserted reliably here; the lossy flag, whose effect isn’t observable from the bitstream alone; and the pixel-format / resource / tuning flags (native_gray, native_16bit, native_f32, enforces_max_pixels / enforces_max_memory, the CICP-carrier flags, and the effort / quality / threads ranges), whose honesty needs format-specific fixtures a generic harness can’t supply. hdr and gain_map have their own checks (check_native_hdr_roundtrip, check_gain_map_roundtrip).