tests: more property based tests, move common fixtures out

sunblock.py

@@ -89,9 +89,11 @@ def process(data: dict[str, Any] | None) -> pd.DataFrame | None:
 
 def find_sun(data: pd.DataFrame, num_hours: int) -> SunblockResult:
     "Finds sun for `num_hours` in the data, after `day_start`"
-    assert (
-        isinstance(num_hours, int) and 0 < num_hours < 23
-    ), "Number of hours must be between 0 and 23"
+    assert isinstance(num_hours, int), "num_hours should be an integer"
+    if num_hours < 1:
+        raise ValueError("Minimum num_hours is 1")
+    if num_hours > 23:
+        raise ValueError("Maximum sun block allowed is 23 hours")
     sunny = (
         (data.sunrise <= data.time)
         & (data.time <= data.sunset)
@@ -103,7 +105,12 @@ def find_sun(data: pd.DataFrame, num_hours: int) -> SunblockResult:
         return SunblockResult(num_hours, None, None, "No sunny interval found")
     else:
         mean_temp = data.loc[idx : idx + num_hours].temperature_celsius.mean()
-        return SunblockResult(num_hours, data.loc[idx].time, mean_temp, "")
+        return SunblockResult(
+            num_hours,
+            datetime.datetime.fromisoformat(data.loc[idx].time),
+            mean_temp,
+            "",
+        )
 
 
 if __name__ == "__main__":

tests/conftest.py

@@ -0,0 +1,13 @@
+"Fixtures common to all tests"
+
+import json
+import pytest
+from pathlib import Path
+
+from sunblock import process
+
+
+@pytest.fixture(scope="session")
+def openmeteo_data():
+    data = json.loads(Path(__file__).with_name("openmeteo.json").read_text())
+    return process(data)

tests/test_examples.py

@@ -13,16 +13,10 @@
     process,
     find_sun,
     SunblockResult,
-    NEWCASTLE
+    NEWCASTLE,
 )
 
 
-@pytest.fixture(scope="session")
-def openmeteo_data():
-    data = json.loads(Path(__file__).with_name("openmeteo.json").read_text())
-    return process(data)
-
-
 def test_openmeteo_url():
     assert openmeteo_api_url(Location(1, -1)) == (
         "https://api.open-meteo.com/v1/forecast?latitude=1&longitude=-1"
@@ -40,6 +34,7 @@ def test_fetch_network():
     assert_approx_equal(data["longitude"], NEWCASTLE[1])
     assert len(data["hourly"]["time"]) == 24 * 7
 
+
 @pytest.mark.parametrize(
     "fahrenheit,expected_celsius",
     [
@@ -67,7 +62,11 @@ def test_process(openmeteo_data):
 def test_find_sun(openmeteo_data):
     block = find_sun(openmeteo_data, num_hours=3)
     assert_approx_equal(block.mean_temp_celsius, 19.916666666666668)
-    assert (block.num_hours, block.start, block.message) == (3, "2024-08-23T11:00", "")
+    assert (block.num_hours, block.start, block.message) == (
+        3,
+        datetime.datetime.fromisoformat("2024-08-23T11:00"),
+        "",
+    )
 
 
 def test_find_sun_not_found(openmeteo_data):

tests/test_property.py

@@ -2,10 +2,14 @@
 Property based testing
 Testing module using hypothesis
 """
+import json
+from pathlib import Path
+
+import pytest
 from hypothesis import given, reject, settings
 from hypothesis.strategies import floats, integers
 
-from sunblock import fahrenheit_to_celsius
+from sunblock import fahrenheit_to_celsius, find_sun
 
 # In property based testing, we encode assumptions or properties of the
 # system that should always be true, regardless of parameter values a
@@ -39,3 +43,20 @@ def test_fahrenheit_differs_from_celsius(temp):
         assert fahrenheit_to_celsius(temp) != temp
     except ValueError:
         reject()
+
+
+# Test that a range of sunblock lengths does not crash the program
+@given(num_hours=integers(min_value=1, max_value=23))
+def test_find_sun(num_hours, openmeteo_data):
+    block = find_sun(openmeteo_data, num_hours)
+    if block.message != "No sunny interval found":
+        assert block.num_hours == num_hours
+        # This is not true everywhere of course, but should be true
+        # for the sample data that we are using here
+        # Ideally the sample data would also be autogenerated, perhaps
+        # using hypothesis-jsonschema and the function tested in a variety
+        # of geographical locations
+        assert 4 <= block.start.time().hour < 23
+
+        # Extremely unlikely in our test sample to have 4h contiguous sun
+        assert num_hours < 4