add robustness tests for ARINC 717/767 bit extraction and decoding

Author: JaskRendix

tests/test_arinc717_parameter.py

@@ -91,3 +91,102 @@ def test_arinc717_cob():
         cob_formula="raw * 0.00390625",
     )
     assert abs(p.decode(256) - 1.0) < 1e-6
+
+
+def test_signed_cross_byte_extraction():
+    # 0b0111_1111_1111_1111 = +32767
+    # 0b1000_0000_0000_0001 = -32767 (two's complement)
+    data_pos = b"\x7F\xFF"
+    data_neg = b"\x80\x01"
+
+    p = Parameter("X", start_bit=0, bit_length=16, data_type="BNR", signed=True)
+
+    assert p.decode_raw_from_bytes(data_pos) == 32767
+    assert p.decode_raw_from_bytes(data_neg) == -32767
+
+
+def test_char_with_embedded_nulls():
+    raw = int.from_bytes(b"A\x00C", "big")
+    p = Parameter("CH", start_bit=0, bit_length=24, data_type="CHAR")
+    assert p.decode(raw) == "A\x00C"
+
+
+def test_utc_leading_zero():
+    p = Parameter("UTC", start_bit=0, bit_length=24, data_type="UTC")
+    assert p.decode(0x012305) == "01:23:05"
+
+
+def test_cob_formula_failure_falls_back_to_raw():
+    p = Parameter(
+        "BAD",
+        start_bit=0,
+        bit_length=8,
+        data_type="COB",
+        cob_formula="raw / 0",  # division by zero
+    )
+    assert p.decode(10) == 10
+
+
+def test_717_decode_from_frame_uses_word_fields():
+    frame = bytes([0x12, 0x34, 0x56])
+    p = Parameter(
+        "ALT",
+        bit_length=8,
+        data_type="BNR",
+        start_bit=None,
+        subframe=0,
+        word=1,
+        bit_offset=0,
+    )
+    # word=1 → second byte → 0x34
+    val, valid = p.decode_from_frame(frame, words_per_subframe=4, word_bits=8)
+    assert valid
+    assert val == 0x34
+
+
+def test_767_decode_raw_requires_start_bit():
+    p = Parameter("X", bit_length=8, data_type="BNR", start_bit=None)
+    with pytest.raises(ValueError):
+        p.decode_raw_from_bytes(b"\x00")
+
+
+def test_717_absolute_bit_start_multi_subframe():
+    p = Parameter(
+        "ALT",
+        bit_length=8,
+        data_type="BNR",
+        start_bit=None,
+        subframe=3,
+        word=2,
+        bit_offset=5,
+    )
+    # subframe 3 → 3 * (4 words * 12 bits) = 144
+    assert p.compute_absolute_bit_start(4, 12) == 144 + 24 + 5
+
+
+def test_767_extract_non_byte_aligned():
+    data = b"\xAA\xBB\xCC"  # 10101010 10111011 11001100
+    p = Parameter("X", start_bit=5, bit_length=10, data_type="DISCRETE")
+    assert p.extract_bits_767(data, 5, 10) == 0b0101011101
+
+
+def test_717_out_of_bounds():
+    frame = b"\x00\x00"
+    p = Parameter(
+        "ALT",
+        bit_length=16,
+        data_type="BNR",
+        start_bit=None,
+        subframe=0,
+        word=1,
+        bit_offset=0,
+    )
+    val, valid = p.decode_from_frame(frame, 4, 12)
+    assert not valid
+    assert val is None
+
+
+def test_767_partial_data_rejected():
+    p = Parameter("X", start_bit=8, bit_length=16, data_type="BNR")
+    with pytest.raises(ValueError):
+        p.decode_raw_from_bytes(b"\x12")  # only 8 bits available

tests/test_arinc767_parameter.py

@@ -97,3 +97,102 @@ def test_arinc767_extract_out_of_bounds_raises() -> None:
     p = Parameter("X", start_bit=32, bit_length=8, data_type="BNR")
     with pytest.raises(ValueError):
         _ = p.decode_raw_from_bytes(b"\x00\x00\x00\x00")
+
+
+def test_signed_cross_byte_extraction():
+    # 0b0111_1111_1111_1111 = +32767
+    # 0b1000_0000_0000_0001 = -32767 (two's complement)
+    data_pos = b"\x7F\xFF"
+    data_neg = b"\x80\x01"
+
+    p = Parameter("X", start_bit=0, bit_length=16, data_type="BNR", signed=True)
+
+    assert p.decode_raw_from_bytes(data_pos) == 32767
+    assert p.decode_raw_from_bytes(data_neg) == -32767
+
+
+def test_char_with_embedded_nulls():
+    raw = int.from_bytes(b"A\x00C", "big")
+    p = Parameter("CH", start_bit=0, bit_length=24, data_type="CHAR")
+    assert p.decode(raw) == "A\x00C"
+
+
+def test_utc_leading_zero():
+    p = Parameter("UTC", start_bit=0, bit_length=24, data_type="UTC")
+    assert p.decode(0x012305) == "01:23:05"
+
+
+def test_cob_formula_failure_falls_back_to_raw():
+    p = Parameter(
+        "BAD",
+        start_bit=0,
+        bit_length=8,
+        data_type="COB",
+        cob_formula="raw / 0",  # division by zero
+    )
+    assert p.decode(10) == 10
+
+
+def test_717_decode_from_frame_uses_word_fields():
+    frame = bytes([0x12, 0x34, 0x56])
+    p = Parameter(
+        "ALT",
+        bit_length=8,
+        data_type="BNR",
+        start_bit=None,
+        subframe=0,
+        word=1,
+        bit_offset=0,
+    )
+    # word=1 → second byte → 0x34
+    val, valid = p.decode_from_frame(frame, words_per_subframe=4, word_bits=8)
+    assert valid
+    assert val == 0x34
+
+
+def test_767_decode_raw_requires_start_bit():
+    p = Parameter("X", bit_length=8, data_type="BNR", start_bit=None)
+    with pytest.raises(ValueError):
+        p.decode_raw_from_bytes(b"\x00")
+
+
+def test_717_absolute_bit_start_multi_subframe():
+    p = Parameter(
+        "ALT",
+        bit_length=8,
+        data_type="BNR",
+        start_bit=None,
+        subframe=3,
+        word=2,
+        bit_offset=5,
+    )
+    # subframe 3 → 3 * (4 words * 12 bits) = 144
+    assert p.compute_absolute_bit_start(4, 12) == 144 + 24 + 5
+
+
+def test_767_extract_non_byte_aligned():
+    data = b"\xAA\xBB\xCC"  # 10101010 10111011 11001100
+    p = Parameter("X", start_bit=5, bit_length=10, data_type="DISCRETE")
+    assert p.extract_bits_767(data, 5, 10) == 0b0101011101
+
+
+def test_717_out_of_bounds():
+    frame = b"\x00\x00"
+    p = Parameter(
+        "ALT",
+        bit_length=16,
+        data_type="BNR",
+        start_bit=None,
+        subframe=0,
+        word=1,
+        bit_offset=0,
+    )
+    val, valid = p.decode_from_frame(frame, 4, 12)
+    assert not valid
+    assert val is None
+
+
+def test_767_partial_data_rejected():
+    p = Parameter("X", start_bit=8, bit_length=16, data_type="BNR")
+    with pytest.raises(ValueError):
+        p.decode_raw_from_bytes(b"\x12")  # only 8 bits available