add a test to check zero index array do not error

closes #21946

Author: illegalnumbers

pandas/tests/indexing/test_indexing.py

@@ -855,6 +855,14 @@ def test_no_reference_cycle(self):
         del df
         assert wr() is None
 
+    def test_no_error_for_zero_index(self):
+      # GH-21946
+      df = DataFrame([[1, 2], [3, 4]], columns=['a', 'b'])
+      ar = np.array(0)
+      try:
+        assert df.iloc[ar].all() == df.iloc[0].all()
+      except TypeError:
+        pytest.fail("Unexpected TypeError, should be first element of array.")
 
 class TestSeriesNoneCoercion(object):
     EXPECTED_RESULTS = [