add test function

Author: facaiy

.gitignore

@@ -18,6 +18,7 @@
 .vagrant
 .noseids
 .ipynb_checkpoints
+.tags
 
 # Compiled source #
 ###################

pandas/tests/frame/test_timeseries.py

@@ -341,3 +341,27 @@ def test_first_last_valid(self):
         empty = DataFrame()
         self.assertIsNone(empty.last_valid_index())
         self.assertIsNone(empty.first_valid_index())
+
+    def test_operation_on_NaT(self):
+        # Both NaT and Timestamp are in DataFrame.
+        df = pd.DataFrame({'foo': [pd.NaT, pd.NaT,
+                                   pd.Timestamp('2012-05-01')]})
+
+        res = df.min()
+        exp = pd.Series([pd.Timestamp('2012-05-01')], index=["foo"])
+        tm.assert_series_equal(res, exp)
+
+        res = df.max()
+        exp = pd.Series([pd.Timestamp('2012-05-01')], index=["foo"])
+        tm.assert_series_equal(res, exp)
+
+        # GH12941, only NaTs are in DataFrame.
+        df = pd.DataFrame({'foo': [pd.NaT, pd.NaT]})
+
+        res = df.min()
+        exp = pd.Series([pd.NaT], index=["foo"])
+        tm.assert_series_equal(res, exp)
+
+        res = df.max()
+        exp = pd.Series([pd.NaT], index=["foo"])
+        tm.assert_series_equal(res, exp)

pandas/tests/test_groupby.py

@@ -720,6 +720,32 @@ def test_agg_period_index(self):
         grouped = df.groupby(df.index.month)
         list(grouped)
 
+    def test_agg_dict_parameter_cast_result_dtypes(self):
+        # GH 12821
+
+        df = DataFrame(
+            {'class': ['A', 'A', 'B', 'B', 'C', 'C', 'D', 'D'],
+             'time': date_range('1/1/2011', periods=8, freq='H')})
+        df.loc[[0, 1, 2, 5], 'time'] = None
+
+        # test for `first` function
+        exp = df.loc[[0, 3, 4, 6]].set_index('class')
+        grouped = df.groupby('class')
+        assert_frame_equal(grouped.first(), exp)
+        assert_frame_equal(grouped.agg('first'), exp)
+        assert_frame_equal(grouped.agg({'time': 'first'}), exp)
+        assert_series_equal(grouped.time.first(), exp['time'])
+        assert_series_equal(grouped.time.agg('first'), exp['time'])
+
+        # test for `last` function
+        exp = df.loc[[0, 3, 4, 7]].set_index('class')
+        grouped = df.groupby('class')
+        assert_frame_equal(grouped.last(), exp)
+        assert_frame_equal(grouped.agg('last'), exp)
+        assert_frame_equal(grouped.agg({'time': 'last'}), exp)
+        assert_series_equal(grouped.time.last(), exp['time'])
+        assert_series_equal(grouped.time.agg('last'), exp['time'])
+
     def test_agg_must_agg(self):
         grouped = self.df.groupby('A')['C']
         self.assertRaises(Exception, grouped.agg, lambda x: x.describe())