Add missing tests for indexes (#692)

 I found that there was not enough exception testing for the names property.

![image](https://user-images.githubusercontent.com/44108233/63647783-526ad900-c761-11e9-8140-61201cdf268e.png)


So I added tests for those exceptions,

And also added tests for some other code that isn't being tested yet.

It's very appreciate it if someone check it out when available. :)

Thanks.

databricks/koalas/tests/test_indexes.py

@@ -22,6 +22,7 @@
 import pyspark
 
 import databricks.koalas as ks
+from databricks.koalas.generic import max_display_count
 from databricks.koalas.exceptions import PandasNotImplementedError
 from databricks.koalas.missing.indexes import _MissingPandasLikeIndex, _MissingPandasLikeMultiIndex
 from databricks.koalas.testing.utils import ReusedSQLTestCase, TestUtils
@@ -55,6 +56,26 @@ def test_index(self):
                 kdf = ks.from_pandas(pdf)
                 self.assert_eq(kdf.index, pdf.index)
 
+    def test_index_getattr(self):
+        kidx = self.kdf.index
+        item = 'databricks'
+
+        expected_error_message = ("'Index' object has no attribute '{}'".format(item))
+        with self.assertRaisesRegex(AttributeError, expected_error_message):
+            kidx.__getattr__(item)
+
+    def test_multi_index_getattr(self):
+        arrays = [[1, 1, 2, 2], ['red', 'blue', 'red', 'blue']]
+        idx = pd.MultiIndex.from_arrays(arrays, names=('number', 'color'))
+        pdf = pd.DataFrame(np.random.randn(4, 5), idx)
+        kdf = ks.from_pandas(pdf)
+        kidx = kdf.index
+        item = 'databricks'
+
+        expected_error_message = ("'MultiIndex' object has no attribute '{}'".format(item))
+        with self.assertRaisesRegex(AttributeError, expected_error_message):
+            kidx.__getattr__(item)
+
     def test_to_series(self):
         pidx = self.pdf.index
         kidx = self.kdf.index
@@ -93,6 +114,14 @@ def test_index_names(self):
         self.assertEqual(kidx.names, pidx.names)
         self.assert_eq(kidx, pidx)
 
+        with self.assertRaisesRegex(ValueError, "Names must be a list-like"):
+            kidx.names = 'hi'
+
+        expected_error_message = ("Length of new names must be {}, got {}"
+                                  .format(len(kdf._internal.index_map), len(['0', '1'])))
+        with self.assertRaisesRegex(ValueError, expected_error_message):
+            kidx.names = ['0', '1']
+
     def test_multi_index_names(self):
         arrays = [[1, 1, 2, 2], ['red', 'blue', 'red', 'blue']]
         idx = pd.MultiIndex.from_arrays(arrays, names=('number', 'color'))

databricks/koalas/tests/test_repr.py

@@ -36,6 +36,16 @@ def test_repr_series(self):
         kser = ks.range(max_display_count + 1).id
         self.assertTrue("Showing only the first" in repr(kser))
 
+    def test_repr_indexes(self):
+        kdf = ks.range(max_display_count)
+        kidx = kdf.index
+        self.assertTrue("Showing only the first" not in repr(kidx))
+        self.assert_eq(repr(kidx), repr(kidx.to_pandas()))
+
+        kdf = ks.range(max_display_count + 1)
+        kidx = kdf.index
+        self.assertTrue("Showing only the first" in repr(kidx))
+
     def test_html_repr(self):
         kdf = ks.range(max_display_count)
         self.assertTrue("Showing only the first" not in kdf._repr_html_())