Adding a test to check that infectious virus removal rate is computed only at the time of a state change

cara/tests/models/test_concentration_model.py

@@ -1,7 +1,10 @@
+from dataclasses import dataclass
+
 import numpy as np
+import numpy.testing as npt
 import pytest
 
-import cara.models
+from cara import models
 
 
 @pytest.mark.parametrize(
@@ -27,28 +30,28 @@ def test_concentration_model_vectorisation(override_params):
     }
     defaults.update(override_params)
 
-    always = cara.models.PeriodicInterval(240, 240)  # TODO: This should be a thing on an interval.
-    c_model = cara.models.ConcentrationModel(
-        cara.models.Room(defaults['volume']),
-        cara.models.AirChange(always, defaults['air_change']),
-        cara.models.InfectedPopulation(
+    always = models.PeriodicInterval(240, 240)  # TODO: This should be a thing on an interval.
+    c_model = models.ConcentrationModel(
+        models.Room(defaults['volume']),
+        models.AirChange(always, defaults['air_change']),
+        models.InfectedPopulation(
             number=1,
             presence=always,
-            mask=cara.models.Mask(
+            mask=models.Mask(
                 η_exhale=defaults['η_exhale'],
                 η_leaks=defaults['η_leaks'],
                 η_inhale=0.3,
             ),
-            activity=cara.models.Activity(
+            activity=models.Activity(
                 0.51,
                 0.75,
             ),
-            virus=cara.models.Virus(
+            virus=models.Virus(
                 halflife=defaults['virus_halflife'],
                 viral_load_in_sputum=defaults['viral_load_in_sputum'],
                 coefficient_of_infectivity=defaults['coefficient_of_infectivity'],
             ),
-            expiration=cara.models.Expiration(
+            expiration=models.Expiration(
                 ejection_factor=(0.084, 0.009, 0.003, 0.002),
             ),
         )
@@ -56,3 +59,76 @@ def test_concentration_model_vectorisation(override_params):
     concentrations = c_model.concentration(10)
     assert isinstance(concentrations, np.ndarray)
     assert concentrations.shape == (2, )
+
+
+@dataclass(frozen=True)
+class DummyVentilation(models.Ventilation):
+    # Dummy ventilation where air_exchange depends on time explicitly
+
+    #: The interval in which the ventilation is operating.
+    active: models.Interval
+
+    def air_exchange(self, room: models.Room, time: float) -> models._VectorisedFloat:
+        if not self.active.triggered(time):
+            return 0.
+        return time*0.5
+
+
+@dataclass(frozen=True)
+class DummyPopulation(models.Population):
+    # Dummy infected population where emission rate depends on time 
+    # explicitly
+    virus: models.Virus
+    expiration: models.Expiration
+
+    def emission_rate_when_present(self) -> models._VectorisedFloat:
+        return 50.
+
+    def individual_emission_rate(self, time) -> models._VectorisedFloat:
+        """
+        The emission rate of a single individual in the population.
+        """
+
+        if not self.person_present(time):
+            return 0.
+
+        return self.emission_rate_when_present()*time
+
+    def emission_rate(self, time) -> models._VectorisedFloat:
+        """
+        The emission rate of the entire population.
+        """
+        return self.individual_emission_rate(time) * self.number
+
+
+def test_concentration_model_constant_parameters():
+    always = models.SpecificInterval(present_times=[(0,24)])
+    c_model = models.ConcentrationModel(
+        models.Room(75),
+        DummyVentilation(always),
+        DummyPopulation(
+            number=1,
+            presence=always,
+            mask=models.Mask(
+                η_exhale=0.95,
+                η_leaks=0.15,
+                η_inhale=0.3,
+            ),
+            activity=models.Activity(
+                0.51,
+                0.75,
+            ),
+            virus=models.Virus(
+                halflife=1.1,
+                viral_load_in_sputum=1e9,
+                coefficient_of_infectivity=0.02,
+            ),
+            expiration=models.Expiration(
+                ejection_factor=(0.084, 0.009, 0.003, 0.002),
+            ),
+        )
+    )
+    times = [0.1, 10, 20, 24]
+    IVRRs = np.array([c_model.infectious_virus_removal_rate(t)
+                      for t in times])
+    assert np.all(IVRRs==IVRRs[-1])