test: pin training-value/isovalue direction agreement for stratigraphic columns

Guards against the swap fixed in 814be12: model_manager.py's per-unit
training value and LoopStructural's get_isovalues() must agree on
which direction values increase, or extracted isosurfaces get labelled
with the wrong unit while keeping correct geometry.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: lachlangrose

tests/qgis/test_stratigraphic_value_consistency.py

@@ -0,0 +1,102 @@
+"""Regression test for the training-value / isovalue direction bug.
+
+`GeologicalModelManager.update_foliation_features` assigns a scalar `val` to
+each unit's basal contact before handing the data to the interpolator.
+`StratigraphicColumn.get_isovalues` (LoopStructural core) later decides which
+name to stamp on each extracted isosurface, using its own idea of which
+value belongs to which unit.
+
+These two must agree on direction (does value increase from oldest-to-
+youngest, or youngest-to-oldest?), or every extracted surface gets labelled
+with the wrong unit while keeping correct geometry -- see the "stratigraphic
+column was reversed" fixes in model_manager.py (2025-07-21) and the widget
+(2025-08-21, reverted 2025-09-08). This has flipped back and forth as this
+plugin and LoopStructural evolved independently; this test pins the
+invariant so a future change on either side fails loudly here instead of
+silently inverting a user's model.
+"""
+
+import pandas as pd
+import pytest
+from LoopStructural import StratigraphicColumn
+
+from loopstructural.main.model_manager import GeologicalModelManager
+
+
+def _contact(unit_name):
+    """A minimal single-point basal contact, tagged with its unit name so
+    the test can recover which row came from which unit after the group
+    DataFrames get concatenated."""
+    return pd.DataFrame({'X': [0.0], 'Y': [0.0], 'Z': [0.0], 'source_unit': [unit_name]})
+
+
+@pytest.fixture
+def manager(monkeypatch):
+    manager = GeologicalModelManager()
+
+    captured_calls = []
+
+    def fake_create_and_add_foliation(name, data=None, **kwargs):
+        captured_calls.append(data)
+        return object()  # stand-in foliation, only passed back into add_unconformity
+
+    monkeypatch.setattr(manager.model, 'create_and_add_foliation', fake_create_and_add_foliation)
+    monkeypatch.setattr(manager.model, 'add_unconformity', lambda *a, **k: None)
+    manager._captured_calls = captured_calls
+    return manager
+
+
+class TestTrainingValueMatchesIsovalue:
+    def test_single_group_three_units(self, manager):
+        column = StratigraphicColumn()
+        column.clear(basement=False)  # single flat group, no unconformities
+        column.add_unit(name='oldest', thickness=100.0, where='top')
+        column.add_unit(name='middle', thickness=200.0, where='top')
+        column.add_unit(name='youngest', thickness=300.0, where='top')
+
+        manager.stratigraphic_column = column
+        for name in ('oldest', 'middle', 'youngest'):
+            manager.stratigraphy[name]['contact'] = _contact(name)
+
+        manager.update_foliation_features()
+
+        training_values = self._training_values_by_unit(manager._captured_calls)
+        expected_values = {
+            name: entry['value'] for name, entry in column.get_isovalues().items()
+        }
+
+        for unit_name in ('oldest', 'middle', 'youngest'):
+            assert training_values[unit_name] == pytest.approx(expected_values[unit_name]), (
+                f"'{unit_name}' was trained with val={training_values[unit_name]} but "
+                f"get_isovalues() will label the value={expected_values[unit_name]} surface "
+                f"with this unit's name -- the trained field and the isosurface labels "
+                f"disagree on direction, so extracted surfaces will get the wrong unit name."
+            )
+
+    def test_two_groups_split_by_unconformity(self, manager):
+        column = StratigraphicColumn()
+        column.clear(basement=False)
+        column.add_unit(name='basin_floor', thickness=50.0, where='top')
+        column.add_unit(name='basin_fill', thickness=150.0, where='top')
+        column.add_unconformity(name='regional_unconformity', where='top')
+        column.add_unit(name='cover_lower', thickness=80.0, where='top')
+        column.add_unit(name='cover_upper', thickness=120.0, where='top')
+
+        manager.stratigraphic_column = column
+        for name in ('basin_floor', 'basin_fill', 'cover_lower', 'cover_upper'):
+            manager.stratigraphy[name]['contact'] = _contact(name)
+
+        manager.update_foliation_features()
+
+        training_values = self._training_values_by_unit(manager._captured_calls)
+        expected_values = {
+            name: entry['value'] for name, entry in column.get_isovalues().items()
+        }
+
+        for unit_name in ('basin_floor', 'basin_fill', 'cover_lower', 'cover_upper'):
+            assert training_values[unit_name] == pytest.approx(expected_values[unit_name])
+
+    @staticmethod
+    def _training_values_by_unit(captured_calls):
+        combined = pd.concat(captured_calls, ignore_index=True)
+        return dict(zip(combined['source_unit'], combined['val']))