Closes #19

tests/README.md

@@ -86,6 +86,22 @@ extended frames may share a numeric ID, and separate frames may reuse signal nam
 Signal tests cover complete syntax and numeric validation, scientific notation,
 finite physical parameters and ordered ranges, spaces and tabs, receiver lists,
 unsupported multiplexing, and Intel/Motorola declared-payload boundaries.
+Physical-number tests apply a custom comma-decimal C++ locale and an available
+named comma-decimal C numeric locale. They check all four physical fields,
+leading signs, fractions, scientific notation, finite boundaries, zero, malformed
+numbers, comma/grouped numbers, overflow/underflow, and reversed ranges. Locale
+changes are restored after each test. The named C locale case skips if none of
+the supported locale names are installed; the custom C++ locale case always runs.
+On Linux with locale sources and `localedef`, run both cases without installing a
+system locale:
+
+```sh
+mkdir -p /tmp/dbc-test-locales
+localedef --no-archive -i de_DE -f UTF-8 /tmp/dbc-test-locales/de_DE.UTF-8
+LOCPATH=/tmp/dbc-test-locales make check
+```
+
+Run `make check` from the build directory as usual.
 Value-description tests cover full `VAL_` syntax, whitespace, escaped quotes,
 empty text, exact integer boundaries, duplicate keys within and across statements,
 deferred and normalized frame references, missing targets, error locations,