test(base64): add QuickCheck round-trip properties - #4007
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Five properties anchored on the encoder's output, all driven by arbitrary `Bytes`: - `decode(encode(b)) == b`, padded and unpadded - padded and unpadded encodings decode to the same bytes - arbitrary ASCII whitespace spliced at arbitrary positions (including between the two `=`) still decodes with `ignore_whitespace=true` - arbitrary non-alphabet characters spliced in are skipped by `decode_lossy` The perturbing splices are driven by a generated `Array[(Int, Int)]` of (position, char-choice) pairs, so placement and count shrink along with the input. Indices are wrapped into range rather than filtered, so no case is discarded.
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Coverage Report for CI Build 5849Coverage increased (+0.03%) to 90.322%Details
Uncovered ChangesNo uncovered changes found. Coverage RegressionsNo coverage regressions found. Coverage Stats
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encoding/base64/quickcheck_test.mbtwith five property-based round-trip tests, plus a test-onlyquickcheckimport inencoding/base64/moon.pkg. No change topkg.generated.mbti.All properties are driven by arbitrary
Bytesand anchored on the encoder's output:encode then decode is the identitydecode(encode(b)) == b… without paddingdecode(encode(b, padding=false)) == bpadded and unpadded encodings decode alikewhitespace anywhere survives the round trip=and after them — still decodes withignore_whitespace=truedecode_lossy round trips through invalid charactersdecode_lossyThe last two use a
splicehelper driven by a generatedArray[(Int, Int)]of (position, char-choice) pairs, so the number and placement of perturbations are themselves generated and shrink with the counterexample. Indices are wrapped into range withwrap_indexrather than filtered, so the driver never discards a case.Verification
moon test -p moonbitlang/core/encoding/base64→ 16 passed, 0 failedmoon check encoding/base64→ cleanmoon info && moon fmt→.mbtiunchanged (test-only change)ignore_whitespace=trueand adding a falsebytes.length() < 3conjunct made both properties fail with shrunk counterexamples ((<Bytes: []>, [(0, 0)], false)and a 3-byte case), confirming the properties are not vacuous and that the spliced edits really reach the decoder.