rename the reduction test (#8)

* correct the name of the variable reduction test to something more accurate

* call the test function `numerical_reduce`

this means we don't have to rename again when we add boolean
reduce (`all`, `any`), cumulative reduce (`cumsum`, `cumprod`),
ordering (`min`, `max`, `median`), and indexing ordering (`argmin`,
`argmax`) tests.

Author: keewis

xarray_array_testing/reduction.py

@@ -15,7 +15,7 @@ def expected_errors(op, **parameters):
 
     @pytest.mark.parametrize("op", ["mean", "sum", "prod", "std", "var"])
     @given(st.data())
-    def test_variable_mean(self, op, data):
+    def test_variable_numerical_reduce(self, op, data):
         variable = data.draw(xrst.variables(array_strategy_fn=self.array_strategy_fn))
 
         with self.expected_errors(op, variable=variable):