TST: Test inplace operations on indexes that require type promotion.

Author: josteinbf

pandas/tests/test_index.py

@@ -1922,6 +1922,33 @@ def test_promote_type(self):
             self.assertEqual(index_promoted.dtype, np.float64)
             self.assertIsInstance(index_promoted, Float64Index)
 
+    def test_promote_type_inplace(self):
+        # Related to GH-9966
+        index = Int64Index(np.arange(5))
+        index += np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index -= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index *= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index /= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
+        index = Int64Index(np.arange(5))
+        index //= np.pi
+        self.assertEqual(index.dtype, np.float64)
+        self.assertIsInstance(index, Float64Index)
+
     def test_equals(self):
 
         i = Float64Index([1.0,2.0])