Parametrize over different reduction operations (#5)

* parametrize over different reduction operations

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---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: TomNicholas

xarray_array_testing/reduction.py

@@ -1,6 +1,7 @@
 from contextlib import nullcontext
 
 import hypothesis.strategies as st
+import pytest
 import xarray.testing.strategies as xrst
 from hypothesis import given
 
@@ -12,22 +13,15 @@ class ReductionTests(DuckArrayTestMixin):
     def expected_errors(op, **parameters):
         return nullcontext()
 
+    @pytest.mark.parametrize("op", ["mean", "sum", "prod", "std", "var"])
     @given(st.data())
-    def test_variable_mean(self, data):
+    def test_variable_mean(self, op, data):
         variable = data.draw(xrst.variables(array_strategy_fn=self.array_strategy_fn))
 
-        with self.expected_errors("mean", variable=variable):
-            actual = variable.mean().data
-            expected = self.xp.mean(variable.data)
-
-        self.assert_equal(actual, expected)
-
-    @given(st.data())
-    def test_variable_prod(self, data):
-        variable = data.draw(xrst.variables(array_strategy_fn=self.array_strategy_fn))
-
-        with self.expected_errors("prod", variable=variable):
-            actual = variable.prod().data
-            expected = self.xp.prod(variable.data)
+        with self.expected_errors(op, variable=variable):
+            # compute using xr.Variable.<OP>()
+            actual = getattr(variable, op)().data
+            # compute using xp.<OP>(array)
+            expected = getattr(self.xp, op)(variable.data)
 
         self.assert_equal(actual, expected)