TST: add tests for keeping dtype in Series.update

pandas/tests/series/test_combine_concat.py

@@ -10,10 +10,10 @@
 import pandas as pd
 from pandas import DataFrame, DatetimeIndex, Series, compat, date_range
 import pandas.util.testing as tm
-from pandas.util.testing import assert_series_equal
+from pandas.util.testing import assert_frame_equal, assert_series_equal
 
 
-class TestSeriesCombine():
+class TestSeriesCombine(object):
 
     def test_append(self, datetime_series, string_series, object_series):
         appendedSeries = string_series.append(object_series)
@@ -116,8 +116,37 @@ def test_update(self):
         df = DataFrame([{"a": 1}, {"a": 3, "b": 2}])
         df['c'] = np.nan
 
-        # this will fail as long as series is a sub-class of ndarray
-        # df['c'].update(Series(['foo'],index=[0])) #####
+        df['c'].update(Series(['foo'], index=[0]))
+        expected = DataFrame([[1, np.nan, 'foo'], [3, 2., np.nan]],
+                             columns=['a', 'b', 'c'])
+        assert_frame_equal(df, expected)
+
+    def test_update_dtypes(self):
+        s = Series([1., 2., False, True])
+        other = Series([45], index=[0])
+        s.update(other)
+
+        expected = Series([45., 2., False, True])
+        assert_series_equal(s, expected)
+
+        t_src = Series([10, 11, 12])
+        t = t_src.copy()
+        other = Series([61, 63], index=[1, 3])
+        t.update(other)
+
+        expected = Series([10, 61, 12])
+        assert_series_equal(t, expected)
+
+        # we always try to keep original dtype, even if other has different one
+        t = t_src.copy()
+        t.update(other.astype(float))
+        assert_series_equal(t, expected)
+
+        # if keeping the dtype is not possible, we allow upcasting
+        t = t_src.copy()
+        t.update(other + 0.1)
+        expected = Series([10., 61.1, 12.])
+        assert_series_equal(t, expected)
 
     def test_concat_empty_series_dtypes_roundtrips(self):