tests: characterize inverter baseclass battery math

tests/batcontrol/inverter/test_inverter_baseclass.py

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+from batcontrol.inverter.baseclass import InverterBaseclass
+
+
+class FakeInverter(InverterBaseclass):
+    def __init__(self, soc, capacity=10000, min_soc=10, max_soc=95):
+        super().__init__({})
+        self._soc = soc
+        self.capacity = capacity
+        self.min_soc = min_soc
+        self.max_soc = max_soc
+
+    def set_mode_force_charge(self, chargerate: float):
+        pass
+
+    def set_mode_avoid_discharge(self):
+        pass
+
+    def set_mode_allow_discharge(self):
+        pass
+
+    def set_mode_limit_battery_charge(self, limit_charge_rate: int):
+        pass
+
+    def get_capacity(self) -> float:
+        return self.capacity
+
+    def get_SOC(self) -> float:
+        return self._soc
+
+    def activate_mqtt(self, api_mqtt_api: object):
+        pass
+
+
+def test_get_stored_energy_uses_soc_percentage():
+    inverter = FakeInverter(soc=65)
+
+    assert inverter.get_stored_energy() == 6500
+
+
+def test_get_stored_energy_floors_negative_result_at_zero():
+    inverter = FakeInverter(soc=-5)
+
+    assert inverter.get_stored_energy() == 0
+
+
+def test_get_stored_usable_energy_subtracts_min_soc():
+    inverter = FakeInverter(soc=65, min_soc=10)
+
+    assert inverter.get_stored_usable_energy() == 5500
+
+
+def test_get_stored_usable_energy_floors_negative_result_at_zero():
+    inverter = FakeInverter(soc=5, min_soc=10)
+
+    assert inverter.get_stored_usable_energy() == 0
+
+
+def test_get_max_capacity_uses_max_soc_limit():
+    inverter = FakeInverter(soc=65, max_soc=95)
+
+    assert inverter.get_max_capacity() == 9500
+
+
+def test_get_usable_capacity_uses_min_and_max_soc_limits():
+    inverter = FakeInverter(soc=65, min_soc=10, max_soc=95)
+
+    assert inverter.get_usable_capacity() == 8500
+
+
+def test_get_free_capacity_can_be_negative_above_max_soc():
+    inverter = FakeInverter(soc=100, max_soc=95)
+
+    assert inverter.get_free_capacity() == -500