TST: Test named aggregations with functions

Closes pandas-dev#28467

Author: gfyoung

pandas/tests/groupby/aggregate/test_aggregate.py

@@ -494,6 +494,43 @@ def test_mangled(self):
         )
         tm.assert_frame_equal(result, expected)
 
+    def test_func_named_agg(self):
+        # see gh-28467
+        animals = DataFrame({
+            "kind": ["cat", "dog", "cat", "dog"],
+            "height": [9.1, 6.0, 9.5, 34.0],
+            "weight": [7.9, 7.5, 9.9, 198.0]
+        })
+
+        result = animals.groupby("kind").agg(
+            mean_height=("height", "mean"),
+            perc90=("height", lambda s: np.percentile(s, q=0.90)))
+        expected = DataFrame([[9.3, 9.1036], [20.0, 6.252]],
+            columns=["mean_height", "perc90"],
+            index=Index(["cat", "dog"], name="kind"))
+
+        tm.assert_frame_equal(result, expected)
+
+    def test_lambda_named_agg2(self):
+        # see gh-28467
+        def myfunc(s):
+            return np.percentile(s, q=0.90)
+
+        animals = DataFrame({
+            "kind": ["cat", "dog", "cat", "dog"],
+            "height": [9.1, 6.0, 9.5, 34.0],
+            "weight": [7.9, 7.5, 9.9, 198.0]
+        })
+
+        result = animals.groupby("kind").agg(
+            mean_height=("height", "mean"),
+            perc90=("height", myfunc))
+        expected = DataFrame([[9.3, 9.1036], [20.0, 6.252]],
+            columns=["mean_height", "perc90"],
+            index=Index(["cat", "dog"], name="kind"))
+
+        tm.assert_frame_equal(result, expected)
+
 
 class TestLambdaMangling:
     def test_maybe_mangle_lambdas_passthrough(self):