Use a custom formula in the higher order formula test

When testing the `FormulaFormatter`, the `microgrid.pv_pool().power` and
`microgrid.grid.power` formulas were used. This pulls a lot of
complexity in, as the whole microgrid needs to be mocked. It also makes
the test nondeterministic, as the components returned by the component
graph, which are used to build the formulas, are returned as a set,
which doesn't provide order, so the resulting formula string will vary
from run to run.

To test higher order formulas, we now build custom formulas instead.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

tests/timeseries/test_formula_formatter.py

@@ -4,15 +4,13 @@
 """Tests for the FormulaFormatter."""
 
 
-from contextlib import AsyncExitStack
-
 from frequenz.channels import Broadcast
 from frequenz.quantities import Quantity
-from pytest_mock import MockerFixture
 
-from frequenz.sdk import microgrid
 from frequenz.sdk.timeseries import Sample
-from frequenz.sdk.timeseries.formula_engine._formula_engine import FormulaBuilder
+from frequenz.sdk.timeseries.formula_engine._formula_engine import (
+    FormulaBuilder,
+)
 from frequenz.sdk.timeseries.formula_engine._formula_formatter import format_formula
 from frequenz.sdk.timeseries.formula_engine._formula_steps import (
     Clipper,
@@ -22,7 +20,6 @@
     Minimizer,
 )
 from frequenz.sdk.timeseries.formula_engine._tokenizer import Tokenizer, TokenType
-from tests.timeseries.mock_microgrid import MockMicrogrid
 
 
 def build_formula(formula: str) -> list[FormulaStep]:
@@ -112,27 +109,34 @@ def test_functions(self) -> None:
         # flake8: enable
         # fmt: on
 
-    async def test_higher_order_formula(self, mocker: MockerFixture) -> None:
-        """Test that the formula is formatted correctly for a higher-order formula."""
-        mockgrid = MockMicrogrid(grid_meter=False, mocker=mocker)
-        mockgrid.add_batteries(3)
-        mockgrid.add_ev_chargers(1)
-        mockgrid.add_solar_inverters(2)
-
-        async with mockgrid, AsyncExitStack() as stack:
-            logical_meter = microgrid.logical_meter()
-            stack.push_async_callback(logical_meter.stop)
-
-            pv_pool = microgrid.new_pv_pool(priority=5)
-            stack.push_async_callback(pv_pool.stop)
-
-            grid = microgrid.grid()
-            stack.push_async_callback(grid.stop)
-
-            assert str(grid.power) == "#36 + #7 + #47 + #17 + #57 + #27"
-
-            composed_formula = (grid.power - pv_pool.power).build("grid_minus_pv")
-            assert (
-                str(composed_formula)
-                == "[grid-power](#36 + #7 + #47 + #17 + #57 + #27) - [pv-power](#47 + #57)"
-            )
+    async def test_higher_order_formula(self) -> None:
+        """Test that higher-order formulas (formulas combining other formulas) are formatted correctly."""
+        # Create two base formulas
+        builder1 = FormulaBuilder("test_formula1", Quantity)
+        builder2 = FormulaBuilder("test_formula2", Quantity)
+
+        # Push metrics directly to the builders
+        channel1 = Broadcast[Sample[Quantity]](name="channel1")
+        channel2 = Broadcast[Sample[Quantity]](name="channel2")
+        builder1.push_metric("#1", channel1.new_receiver(), nones_are_zeros=True)
+        builder1.push_oper("+")
+        builder1.push_metric("#2", channel2.new_receiver(), nones_are_zeros=True)
+
+        channel3 = Broadcast[Sample[Quantity]](name="channel3")
+        channel4 = Broadcast[Sample[Quantity]](name="channel4")
+        builder2.push_metric("#3", channel3.new_receiver(), nones_are_zeros=True)
+        builder2.push_oper("+")
+        builder2.push_metric("#4", channel4.new_receiver(), nones_are_zeros=True)
+
+        # Build individual formula engines first
+        engine1 = builder1.build()
+        engine2 = builder2.build()
+
+        # Combine them into a higher-order formula
+        composed_formula = (engine1 - engine2).build("higher_order_formula")
+
+        # Check the string representation
+        assert (
+            str(composed_formula)
+            == "[test_formula1](#1 + #2) - [test_formula2](#3 + #4)"
+        )