ML-009: add explainable predictions

Closes #20

tests/ml/test_explanation.py

@@ -0,0 +1,34 @@
+from __future__ import annotations
+
+from app.ml.explanation import explain_feature
+from app.ml.training import FeatureModel
+
+
+def _model(slope: float) -> FeatureModel:
+    return FeatureModel(
+        sample_count=4,
+        mean=20.0,
+        standard_deviation=1.0,
+        minimum=18.0,
+        maximum=22.0,
+        slope=slope,
+        intercept=18.5,
+    )
+
+
+def test_explain_feature_describes_rising_forecast() -> None:
+    explanation = explain_feature("temperature", 21.0, 21.5, _model(0.5))
+
+    assert explanation.direction == "steigend"
+    assert explanation.change == 0.5
+    assert explanation.historical_range == (18.0, 22.0)
+    assert "4 Messwerte" in explanation.summary
+    assert "Trend +0.500" in explanation.summary
+
+
+def test_explain_feature_describes_stable_and_falling_forecasts() -> None:
+    stable = explain_feature("humidity", 50.0, 50.0, _model(0.0))
+    falling = explain_feature("temperature", 21.0, 20.5, _model(-0.5))
+
+    assert stable.direction == "stabil"
+    assert falling.direction == "fallend"

tests/ml/test_predictor.py

@@ -33,6 +33,11 @@ def test_predict_returns_statistical_forecast() -> None:
     assert result.predictions == {"temperature": 22.0}
     assert 0.0 < result.confidence <= 1.0
     assert result.model_type == "statistical_baseline"
+    explanation = result.explanations["temperature"]
+    assert explanation.direction == "steigend"
+    assert explanation.current_value == 21.0
+    assert explanation.predicted_value == 22.0
+    assert explanation.sample_count == 2
 
 
 def test_predict_rejects_unknown_sensor() -> None: