Add property-based testing with Hypothesis#636
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Add 48 property-based tests using Hypothesis covering: - Roundtrip tests for all getter/setter pairs (integers, floats, strings, dates) - Roundtrip tests for S7 data type encode/decode - TPKT/COTP frame structure validation - S7 PDU structure validation - Fuzz tests for robustness against malformed input Bugs found and fixed: - set_date: used signed int16 (>h) for days offset, overflows for dates after ~2079. Fixed to unsigned int16 (>H). - set_tod: used float arithmetic (total_seconds() * 1000) causing precision loss. Fixed to use integer arithmetic on timedelta components. Known issue documented (not fixed): - wstring get/set uses character count but UTF-16-BE surrogate pairs for supplementary characters (codepoint > 0xFFFF) need 4 bytes per character. Closes #629 Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
PLCs only support BMP characters (U+0000–U+FFFF) in WSTRING. Characters above U+FFFF require UTF-16 surrogate pairs (4 bytes) but the WSTRING length field counts 2-byte code units, causing data corruption. Validate input and raise ValueError for non-BMP characters, matching the reference PLC implementation behavior. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
get_dtl was reading only byte 8 as a raw integer for microseconds, but the DTL format stores nanoseconds as a 4-byte big-endian uint32 in bytes 8-11. This fix reads the full field and converts ns to us. Also removes unnecessary KeyError catch from PDU fuzz test. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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Summary
set_dateoverflow: used signed>hfor days offset from 1990-01-01, which overflows for dates after ~2079. Fixed to unsigned>H.set_todprecision loss: usedint(total_seconds() * 1000)which loses precision due to float arithmetic. Fixed to integer arithmetic ontimedeltacomponents.set_wstring/get_wstringuse character count, not UTF-16 code unit count.Test coverage
Run with:
pytest -m hypothesisTest plan
pytest -m hypothesismarker worksCloses #629
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