Closes #24

tests/README.md

@@ -152,6 +152,18 @@ and source lifetime, physical conversion, and TypeFactory registration/creation.
 Direct resolver tests construct ambiguous databases through the public metadata
 API, verify source locations, and check that ambiguous targets receive no values.
 
+J1939 regressions in `dbc_coverage_test.cpp` verify explicit parser opt-in and
+ordinary extended CAN defaults, PF 239/240 and all data-page combinations, PGN
+zero, PDU1 destination exclusion, PDU2 group-extension matching, changed source
+and priority, standard/invalid-ID exclusion, and inconsistent manual metadata.
+They also cover exact-ID precedence, order-independent ambiguous PGNs for both
+PDU formats, mixed ordinary/J1939 definitions, selected-signal definition keys,
+raw/physical values, and owning PGN handles across snapshot replacement.
+The pipeline fixture explicitly enables J1939 through the diagnostic parser API.
+Verified in `build/` with `qmake6 ../dbc.pro`, `make -j4`, and `make check`:
+all six QtTest suites and the Qt-free tree target passed. The existing named
+comma-decimal C locale regression skipped because that locale is not installed.
+
 All QtTest targets use Qt 6.8.2 and `QVERIFY_THROWS_EXCEPTION`. Exception tests
 explicitly discard `nodiscard` results when only the exception is being checked.
 The standalone tree test requires only a C++17 compiler.