Refactor test_combine_first dataframe (#63295)

Author: Tsmith-77

pandas/tests/frame/methods/test_combine_first.py

@@ -30,17 +30,19 @@ def test_combine_first_mixed(self):
         combined = f.combine_first(g)
         tm.assert_frame_equal(combined, exp)
 
-    def test_combine_first(self, float_frame):
-        # disjoint
+    def test_combine_first_disjoint(self, float_frame):
         head, tail = float_frame[:5], float_frame[5:]
-
         combined = head.combine_first(tail)
         reordered_frame = float_frame.reindex(combined.index)
+
         tm.assert_frame_equal(combined, reordered_frame)
         tm.assert_index_equal(combined.columns, float_frame.columns)
         tm.assert_series_equal(combined["A"], reordered_frame["A"])
 
-        # same index
+        tm.assert_series_equal(combined["A"].reindex(head.index), head["A"])
+        tm.assert_series_equal(combined["A"].reindex(tail.index), tail["A"])
+
+    def test_combine_first_same_index(self, float_frame):
         fcopy = float_frame.copy()
         fcopy["A"] = 1
         del fcopy["C"]
@@ -56,36 +58,36 @@ def test_combine_first(self, float_frame):
         tm.assert_series_equal(combined["C"], fcopy2["C"])
         tm.assert_series_equal(combined["D"], fcopy["D"])
 
-        # overlap
-        head, tail = reordered_frame[:10].copy(), reordered_frame
+    def test_combine_first_overlap(self, float_frame):
+        combined = float_frame[:5].combine_first(float_frame[5:])
+        reordered_frame = float_frame.reindex(combined.index)
+        head, tail = reordered_frame[:10].copy(), reordered_frame.copy()
         head["A"] = 1
-
         combined = head.combine_first(tail)
         assert (combined["A"][:10] == 1).all()
 
-        # reverse overlap
+    def test_combine_first_reverse_overlap(self, float_frame):
+        combined = float_frame[:5].combine_first(float_frame[5:])
+        reordered_frame = float_frame.reindex(combined.index)
+        head, tail = reordered_frame[:10].copy(), reordered_frame
+
         tail.iloc[:10, tail.columns.get_loc("A")] = 0
         combined = tail.combine_first(head)
         assert (combined["A"][:10] == 0).all()
 
-        # no overlap
-        f = float_frame[:10]
-        g = float_frame[10:]
-        combined = f.combine_first(g)
-        tm.assert_series_equal(combined["A"].reindex(f.index), f["A"])
-        tm.assert_series_equal(combined["A"].reindex(g.index), g["A"])
-
-        # corner cases
+    def test_combine_first_with_empty(self, float_frame):
         comb = float_frame.combine_first(DataFrame())
         tm.assert_frame_equal(comb, float_frame)
 
         comb = DataFrame().combine_first(float_frame)
         tm.assert_frame_equal(comb, float_frame.sort_index())
 
+    def test_combine_first_with_new_index(self, float_frame):
         comb = float_frame.combine_first(DataFrame(index=["faz", "boo"]))
         assert "faz" in comb.index
 
-        # #2525
+    def test_combine_first_column_union(self):
+        # GH#2525
         df = DataFrame({"a": [1]}, index=[datetime(2012, 1, 1)])
         df2 = DataFrame(columns=["b"])
         result = df.combine_first(df2)