TST: categorical reindex with added categories (#43210)

* TST: categorical reindex with added categories

* Update test_reindex.py

* TST: Dataframe construct from series.

Author: Sheogorath27

pandas/tests/frame/test_constructors.py

@@ -43,6 +43,7 @@
     Series,
     Timedelta,
     Timestamp,
+    cut,
     date_range,
     isna,
 )
@@ -2353,6 +2354,32 @@ def test_construct_with_two_categoricalindex_series(self):
         )
         tm.assert_frame_equal(result, expected)
 
+    def test_constructor_series_nonexact_categoricalindex(self):
+        # GH 42424
+        ser = Series(range(0, 100))
+        ser1 = cut(ser, 10).value_counts().head(5)
+        ser2 = cut(ser, 10).value_counts().tail(5)
+        result = DataFrame({"1": ser1, "2": ser2})
+        index = CategoricalIndex(
+            [
+                Interval(-0.099, 9.9, closed="right"),
+                Interval(9.9, 19.8, closed="right"),
+                Interval(19.8, 29.7, closed="right"),
+                Interval(29.7, 39.6, closed="right"),
+                Interval(39.6, 49.5, closed="right"),
+                Interval(49.5, 59.4, closed="right"),
+                Interval(59.4, 69.3, closed="right"),
+                Interval(69.3, 79.2, closed="right"),
+                Interval(79.2, 89.1, closed="right"),
+                Interval(89.1, 99, closed="right"),
+            ],
+            ordered=True,
+        )
+        expected = DataFrame(
+            {"1": [10] * 5 + [np.nan] * 5, "2": [np.nan] * 5 + [10] * 5}, index=index
+        )
+        tm.assert_frame_equal(expected, result)
+
     def test_from_M8_structured(self):
         dates = [(datetime(2012, 9, 9, 0, 0), datetime(2012, 9, 8, 15, 10))]
         arr = np.array(dates, dtype=[("Date", "M8[us]"), ("Forecasting", "M8[us]")])

pandas/tests/indexes/categorical/test_reindex.py

@@ -6,6 +6,7 @@
     CategoricalIndex,
     DataFrame,
     Index,
+    Interval,
     Series,
 )
 import pandas._testing as tm
@@ -103,3 +104,22 @@ def test_reindex_not_category(self, index_df, index_res, index_exp):
         result = df.reindex(index=index_res)
         expected = DataFrame(index=index_exp)
         tm.assert_frame_equal(result, expected)
+
+    def test_reindex_categorical_added_category(self):
+        # GH 42424
+        ci = CategoricalIndex(
+            [Interval(0, 1, closed="right"), Interval(1, 2, closed="right")],
+            ordered=True,
+        )
+        ci_add = CategoricalIndex(
+            [
+                Interval(0, 1, closed="right"),
+                Interval(1, 2, closed="right"),
+                Interval(2, 3, closed="right"),
+                Interval(3, 4, closed="right"),
+            ],
+            ordered=True,
+        )
+        result, _ = ci.reindex(ci_add)
+        expected = ci_add
+        tm.assert_index_equal(expected, result)