Don't crash on fast calculations

bw_aggregation/estimator.py

@@ -4,7 +4,6 @@
 from bw2calc import LCA
 from bw2data import Database, prepare_lca_inputs
 
-from .calculator import AggregationCalculator
 from .override import AggregationContext
 
 
@@ -27,7 +26,8 @@ def difference(self) -> Speedup:
         with_ = self.calculate_with_speedup()
         return Speedup(
             database_name=self.name,
-            time_difference_relative=with_ / without,
+            # Timer on Windows is coarse, could be zero for small databases
+            time_difference_relative=(with_ / without if without > 0 else 0),
             time_difference_absolute=with_ - without,
             time_with_aggregation=with_,
             time_without_aggregation=without,

tests/test_estimation.py

@@ -1,15 +1,10 @@
 import sys
 
-import pytest
-
 from bw_aggregation import AggregatedDatabase, Speedup
 
 
-@pytest.mark.skipif(
-    sys.platform.startswith("win"),
-    reason="Windows `time` function has too low resolution",
-)
 def test_speedup_estimate(background):
     speedup = AggregatedDatabase.estimate_speedup("a")
     assert isinstance(speedup, Speedup)
-    assert speedup.time_difference_relative < 1
+    if not sys.platform.startswith("win"):
+        assert speedup.time_difference_relative < 1