Add more formula tests for min and max functions (#623)

Also we make the interface public as it's considered ready to use.

Author: matthias-wende-frequenz

RELEASE_NOTES.md

@@ -27,11 +27,12 @@
   - Provide access to `capacity` (maximum number of elements) in `MovingWindow`.
   - Methods to retrieve oldest and newest timestamp of valid samples are added to both.
 
-
 - Now when printing `FormulaEngine` for debugging purposes the the formula will be shown in infix notation, which should be easier to read.
 
 - The CI now runs cross-arch tests on `arm64` architectures.
 
+- The `min` and `max` functions in the `FormulaEngine` are now public. Note that the same functions have been public in the builder.
+
 ## Bug Fixes
 
 <!-- Here goes notable bug fixes that are worth a special mention or explanation -->

src/frequenz/sdk/timeseries/_formula_engine/_formula_engine.py

@@ -165,7 +165,7 @@ def __truediv__(
         """
         return self._higher_order_builder(self, self._create_method) / other  # type: ignore
 
-    def _max(
+    def max(
         self, other: _GenericEngine | _GenericHigherOrderBuilder | QuantityT
     ) -> _GenericHigherOrderBuilder:
         """Return a formula engine that outputs the maximum of `self` and `other`.
@@ -180,7 +180,7 @@ def _max(
         """
         return self._higher_order_builder(self, self._create_method).max(other)  # type: ignore
 
-    def _min(
+    def min(
         self, other: _GenericEngine | _GenericHigherOrderBuilder | QuantityT
     ) -> _GenericHigherOrderBuilder:
         """Return a formula engine that outputs the minimum of `self` and `other`.

tests/timeseries/_formula_engine/test_formula_composition.py

@@ -171,18 +171,68 @@ async def test_formula_composition_missing_bat(self, mocker: MockerFixture) -> N
         assert count == 10
 
     async def test_formula_composition_min_max(self, mocker: MockerFixture) -> None:
-        """Test the composition of formulas with min/max values."""
+        """Test the composition of formulas with the min and max."""
         mockgrid = MockMicrogrid(grid_meter=True)
+        mockgrid.add_chps(1)
         await mockgrid.start(mocker)
 
         logical_meter = microgrid.logical_meter()
-        engine_min = logical_meter.grid_power._min(  # pylint: disable=protected-access
-            Power.zero()
-        ).build("grid_power_min")
+        engine_min = logical_meter.grid_power.min(logical_meter.chp_power).build(
+            "grid_power_min"
+        )
+        engine_min_rx = engine_min.new_receiver()
+        engine_max = logical_meter.grid_power.max(logical_meter.chp_power).build(
+            "grid_power_max"
+        )
+        engine_max_rx = engine_max.new_receiver()
+
+        await mockgrid.mock_resampler.send_meter_power([100.0, 200.0])
+
+        # Test min
+        min_pow = await engine_min_rx.receive()
+        assert (
+            min_pow and min_pow.value and min_pow.value.isclose(Power.from_watts(100.0))
+        )
+
+        # Test max
+        max_pow = await engine_max_rx.receive()
+        assert (
+            max_pow and max_pow.value and max_pow.value.isclose(Power.from_watts(200.0))
+        )
+
+        await mockgrid.mock_resampler.send_meter_power([-100.0, -200.0])
+
+        # Test min
+        min_pow = await engine_min_rx.receive()
+        assert (
+            min_pow
+            and min_pow.value
+            and min_pow.value.isclose(Power.from_watts(-200.0))
+        )
+
+        # Test max
+        max_pow = await engine_max_rx.receive()
+        assert (
+            max_pow
+            and max_pow.value
+            and max_pow.value.isclose(Power.from_watts(-100.0))
+        )
+
+        await engine_min._stop()  # pylint: disable=protected-access
+        await mockgrid.cleanup()
+        await logical_meter.stop()
+
+    async def test_formula_composition_min_max_const(
+        self, mocker: MockerFixture
+    ) -> None:
+        """Test the compositing formulas and constants with the min and max functions."""
+        mockgrid = MockMicrogrid(grid_meter=True)
+        await mockgrid.start(mocker)
+
+        logical_meter = microgrid.logical_meter()
+        engine_min = logical_meter.grid_power.min(Power.zero()).build("grid_power_min")
         engine_min_rx = engine_min.new_receiver()
-        engine_max = logical_meter.grid_power._max(  # pylint: disable=protected-access
-            Power.zero()
-        ).build("grid_power_max")
+        engine_max = logical_meter.grid_power.max(Power.zero()).build("grid_power_max")
         engine_max_rx = engine_max.new_receiver()
 
         await mockgrid.mock_resampler.send_meter_power([100.0])

tests/timeseries/test_formula_engine.py

@@ -439,6 +439,78 @@ async def test_simple(self) -> None:
             ],
         )
 
+    async def test_min_max(self) -> None:
+        """Test min and max functions in combination."""
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: c2.min(c4).max(c5),
+            [
+                ([4.0, 6.0, 5.0], 5.0),
+            ],
+        )
+
+    async def test_max(self) -> None:
+        """Test the max function."""
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: c2 * c4.max(c5),
+            [
+                ([10.0, 12.0, 15.0], 150.0),
+            ],
+        )
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: (c2 * c4).max(c5),
+            [
+                ([10.0, 12.0, 15.0], 120.0),
+            ],
+        )
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: (c2 + c4).max(c5),
+            [
+                ([10.0, 12.0, 15.0], 22.0),
+            ],
+        )
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: c2 + c4.max(c5),
+            [
+                ([10.0, 12.0, 15.0], 25.0),
+            ],
+        )
+
+    async def test_min(self) -> None:
+        """Test the min function."""
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: (c2 * c4).min(c5),
+            [
+                ([10.0, 12.0, 15.0], 15.0),
+            ],
+        )
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: c2 * c4.min(c5),
+            [
+                ([10.0, 12.0, 15.0], 120.0),
+            ],
+        )
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: (c2 + c4).min(c5),
+            [
+                ([10.0, 2.0, 15.0], 12.0),
+            ],
+        )
+        await self.run_test(
+            3,
+            lambda c2, c4, c5: c2 + c4.min(c5),
+            [
+                ([10.0, 12.0, 15.0], 22.0),
+            ],
+        )
+
     async def test_compound(self) -> None:
         """Test compound formulas."""
         await self.run_test(