correct def get_start_end_field

Author: natmokval

pandas/_libs/tslibs/fields.pyx

@@ -253,8 +253,7 @@ def get_start_end_field(
         # month of year. Other offsets use month, startingMonth as ending
         # month of year.
 
-        if (freq_name.lstrip("B")[0:2] in ["MS", "QS", "YS"]) or (
-                freq_name.lstrip("CB")[0:2] in ["MS", "QS", "YS"]):
+        if freq_name[0:2]  in ["MS", "QS", "YS"]:
             end_month = 12 if month_kw == 1 else month_kw - 1
             start_month = month_kw
         else:

pandas/tests/indexes/datetimes/test_scalar_compat.py

@@ -345,6 +345,5 @@ def test_dti_is_year_start_freq_custom_business_day_with_digit(self):
             dr.is_year_start
 
     def test_dti_is_year_start_freq_business_month_start_with(self):
-        dr = date_range("2020-01-01", periods=1, freq="CBMS")
-        print(dr.is_year_start)
-        # assert all(dr.is_year_start)
+        dr = date_range("2020-01-01", periods=1, freq="BMS")
+        assert all(dr.is_year_start)