TST: Add tests for old issues

pandas/tests/apply/test_frame_apply.py

@@ -1519,3 +1519,11 @@ def test_apply_np_reducer(float_frame, op, how):
         getattr(np, op)(float_frame, axis=0, **kwargs), index=float_frame.columns
     )
     tm.assert_series_equal(result, expected)
+
+
+def test_apply_getitem_axis_1():
+    # GH 13427
+    df = DataFrame({"a": [0, 1, 2], "b": [1, 2, 3]})
+    result = df[["a", "a"]].apply(lambda x: x[0] + x[1], axis=1)
+    expected = Series([0, 2, 4])
+    tm.assert_series_equal(result, expected)

pandas/tests/frame/methods/test_drop.py

@@ -481,3 +481,12 @@ def test_drop_with_duplicate_columns2(self):
         df2 = df.take([2, 0, 1, 2, 1], axis=1)
         result = df2.drop("C", axis=1)
         tm.assert_frame_equal(result, expected)
+
+    def test_drop_inplace_no_leftover_column_reference(self):
+        # GH 13934
+        df = DataFrame({"a": [1, 2, 3]})
+        a = df.a
+        df.drop(["a"], axis=1, inplace=True)
+        tm.assert_index_equal(df.columns, Index([], dtype="object"))
+        a -= a.mean()
+        tm.assert_index_equal(df.columns, Index([], dtype="object"))

pandas/tests/frame/test_reductions.py

@@ -1638,3 +1638,12 @@ def test_groupy_regular_arithmetic_equivalent(meth):
 
     result = getattr(df.groupby(level=0), meth)(numeric_only=False)
     tm.assert_frame_equal(result, expected)
+
+
+@pytest.mark.parametrize("ts_value", [Timestamp("2000-01-01"), pd.NaT])
+def test_frame_mixed_numeric_object_with_timestamp(ts_value):
+    # GH 13912
+    df = DataFrame({"a": [1], "b": [1.1], "c": ["foo"], "d": [ts_value]})
+    result = df.sum()
+    expected = Series([1, 1.1, "foo"], index=list("abc"))
+    tm.assert_series_equal(result, expected)

pandas/tests/frame/test_stack_unstack.py

@@ -2018,3 +2018,18 @@ def test_stack_nan_level(self):
             ),
         )
         tm.assert_frame_equal(result, expected)
+
+    def test_unstack_categorical_columns(self):
+        # GH 14018
+        idx = MultiIndex.from_product([["A"], [0, 1]])
+        df = DataFrame({"cat": pd.Categorical(["a", "b"])}, index=idx)
+        result = df.unstack()
+        expected = DataFrame(
+            {
+                0: pd.Categorical(["a"], categories=["a", "b"]),
+                1: pd.Categorical(["b"], categories=["a", "b"]),
+            },
+            index=["A"],
+        )
+        expected.columns = MultiIndex.from_tuples([("cat", 0), ("cat", 1)])
+        tm.assert_frame_equal(result, expected)

pandas/tests/indexes/base_class/test_setops.py

@@ -247,3 +247,15 @@ def test_union_name_preservation(
         else:
             expected = Index(vals, name=expected_name)
             tm.equalContents(union, expected)
+
+    @pytest.mark.parametrize(
+        "diff_type, expected",
+        [["difference", [1, "B"]], ["symmetric_difference", [1, 2, "B", "C"]]],
+    )
+    def test_difference_object_type(self, diff_type, expected):
+        # GH 13432
+        idx1 = Index([0, 1, "A", "B"])
+        idx2 = Index([0, 2, "A", "C"])
+        result = getattr(idx1, diff_type)(idx2)
+        expected = Index(expected)
+        tm.assert_index_equal(result, expected)

pandas/tests/indexing/multiindex/test_loc.py

@@ -788,3 +788,16 @@ def test_mi_columns_loc_list_label_order():
         columns=MultiIndex.from_tuples([("B", 1), ("B", 2), ("A", 1), ("A", 2)]),
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_mi_partial_indexing_list_raises():
+    # GH 13501
+    frame = DataFrame(
+        np.arange(12).reshape((4, 3)),
+        index=[["a", "a", "b", "b"], [1, 2, 1, 2]],
+        columns=[["Ohio", "Ohio", "Colorado"], ["Green", "Red", "Green"]],
+    )
+    frame.index.names = ["key1", "key2"]
+    frame.columns.names = ["state", "color"]
+    with pytest.raises(KeyError, match="\\[2\\] not in index"):
+        frame.loc[["b", 2], "Colorado"]

pandas/tests/indexing/test_chaining_and_caching.py

@@ -499,3 +499,10 @@ def test_iloc_setitem_chained_assignment(self):
 
             df["bb"].iloc[0] = 0.15
             assert df["bb"].iloc[0] == 0.15
+
+    def test_getitem_loc_assignment_slice_state(self):
+        # GH 13569
+        df = DataFrame({"a": [10, 20, 30]})
+        df["a"].loc[4] = 40
+        tm.assert_frame_equal(df, DataFrame({"a": [10, 20, 30]}))
+        tm.assert_series_equal(df["a"], Series([10, 20, 30], name="a"))

pandas/tests/io/test_common.py

@@ -2,6 +2,7 @@
 Tests for the pandas.io.common functionalities
 """
 import codecs
+import errno
 from functools import partial
 from io import (
     BytesIO,
@@ -519,3 +520,10 @@ def test_bad_encdoing_errors():
     with tm.ensure_clean() as path:
         with pytest.raises(ValueError, match="Invalid value for `encoding_errors`"):
             icom.get_handle(path, "w", errors="bad")
+
+
+def test_errno_attribute():
+    # GH 13872
+    with pytest.raises(FileNotFoundError, match="\\[Errno 2\\]") as err:
+        pd.read_csv("doesnt_exist")
+        assert err.errno == errno.ENOENT