tests: compare the Farsite model with the FARSITE reference

TESTING.md

@@ -214,6 +214,15 @@ absent. `run.bash` runs it after the examples.
 python3 tests/python/test_validate.py
 ```
 
+`tests/python/test_farsite_reference.py` compares the Farsite model with the
+FARSITE reference code (`mbedward/farsite`) over the 13 fuel models. It needs
+a C++ compiler and is not run by CI. Gaps on slope and at flank/back are
+reported; `--strict` makes the slope gap fail.
+
+```bash
+./.venv/bin/python tests/python/test_farsite_reference.py
+```
+
 `tests/python/` also holds `idealizedwind.py`, `farsite_flat.py` and
 `percolation.py`. They are examples rather than tests — they produce plots and
 assert nothing — and are not run anywhere. They are the closest thing to

tests/python/README.md

@@ -55,6 +55,20 @@ python tests/python/test_moisture_invariants.py        # -v for every probe
 
 `--model NAME` and `--test NAME`, both repeatable, narrow it down.
 
+### `test_farsite_reference.py`
+
+Compares the `Farsite` model with FARSITE's own code for the 13 standard fuel
+models, four midflame winds, three slopes and three moisture sets. The
+reference is `farsite_reference.cpp`, FARSITE's spread rate and ellipse copied
+from mbedward/farsite and compiled by the test with the system C++ compiler.
+Fails when the head rate of spread differs from the reference; flank, back and
+the gap on a slope are printed, not asserted (`--strict` asserts the slope
+too). Needs a C++ compiler besides `pyforefire`. Manually:
+
+```bash
+python tests/python/test_farsite_reference.py        # -v for every case
+```
+
 ### `test_runner.py`
 
 Checks `pyforefire.ForeFireRunner`: eight simulations, each in its own worker