Add OrderHistory.time_step property

src/urban_meal_delivery/forecasts/timify.py

@@ -39,6 +39,11 @@ class OrderHistory:
         # The `_data` are populated by `.aggregate_orders()`.
         self._data = None
 
+    @property
+    def time_step(self) -> int:
+        """The length of one time step."""
+        return self._time_step
+
     @property
     def totals(self) -> pd.DataFrame:
         """The order totals by `Pixel` and `.time_step`.

tests/forecasts/timify/test_order_history.py

@@ -6,33 +6,43 @@ from tests import config as test_config
 from urban_meal_delivery.forecasts import timify
 
 
+@pytest.fixture
+def order_history(grid):
+    """An `OrderHistory` object."""
+    return timify.OrderHistory(grid=grid, time_step=test_config.LONG_TIME_STEP)
+
+
 class TestSpecialMethods:
     """Test the special methods in `OrderHistory`."""
 
-    @pytest.mark.parametrize('time_step', test_config.TIME_STEPS)
+    def test_instantiate(self, order_history):
-    def test_instantiate(self, grid, time_step):
         """Test `OrderHistory.__init__()`."""
-        oh = timify.OrderHistory(grid=grid, time_step=time_step)
+        assert order_history is not None
-
-        assert oh is not None
 
 
 class TestProperties:
     """Test the properties in `OrderHistory`."""
 
-    def test_totals_is_cached(self, grid, monkeypatch):
+    @pytest.mark.parametrize('time_step', test_config.TIME_STEPS)
-        """Test `.totals` property.
+    def test_time_step(self, grid, time_step):
+        """Test `OrderHistory.time_step` property."""
+        order_history = timify.OrderHistory(grid=grid, time_step=time_step)
+
+        result = order_history.time_step
+
+        assert result == time_step
+
+    def test_totals_is_cached(self, order_history, monkeypatch):
+        """Test `OrderHistory.totals` property.
 
         The result of the `OrderHistory.aggregate_orders()` method call
         is cached in the `OrderHistory.totals` property.
         """
-        oh = timify.OrderHistory(grid=grid, time_step=test_config.LONG_TIME_STEP)
-
         sentinel = object()
-        monkeypatch.setattr(oh, 'aggregate_orders', lambda: sentinel)
+        monkeypatch.setattr(order_history, 'aggregate_orders', lambda: sentinel)
 
-        result1 = oh.totals
+        result1 = order_history.totals
-        result2 = oh.totals
+        result2 = order_history.totals
 
         assert result1 is result2
         assert result1 is sentinel