TST: Add tests for all None

Test exception is hit when all values in an object column are None
Extend the test for strl conversion to ensure this case passes (as expected)

Author: bashtage

pandas/tests/io/test_stata.py

@@ -1514,11 +1514,34 @@ def test_mixed_string_strl(self):
             {'mixed': None,
              'number': 1}
         ]
-
         output = pd.DataFrame(output)
+        output.number = output.number.astype('int32')
+
         with tm.ensure_clean() as path:
             output.to_stata(path, write_index=False, version=117)
             reread = read_stata(path)
             expected = output.fillna('')
-            expected.number = expected.number.astype('int32')
             tm.assert_frame_equal(reread, expected)
+
+            # Check strl supports all None (null)
+            output.loc[:, 'mixed'] = None
+            output.to_stata(path, write_index=False, convert_strl=['mixed'],
+                            version=117)
+            reread = read_stata(path)
+            expected = output.fillna('')
+            tm.assert_frame_equal(reread, expected)
+
+    @pytest.mark.parametrize('version', [114, 117])
+    def test_all_none_exception(self, version):
+        output = [
+            {'none': 'none',
+             'number': 0},
+            {'none': None,
+             'number': 1}
+        ]
+        output = pd.DataFrame(output)
+        output.loc[:, 'none'] = None
+        with tm.ensure_clean() as path:
+            with pytest.raises(ValueError) as excinfo:
+                output.to_stata(path, version=version)
+        assert 'Only string-like' in excinfo.value.args[0]