versionadded, fix tests

Author: Joeperdefloep

pandas/io/excel/_base.py

@@ -680,7 +680,7 @@ class ExcelWriter(metaclass=abc.ABCMeta):
         host, port, username, password, etc., if using a URL that will
         be parsed by ``fsspec``, e.g., starting "s3://", "gcs://".
 
-        .. versionadded:: 1.2.0
+        .. versionadded:: 1.4.0
     if_sheet_exists : {'error', 'new', 'replace', 'overwrite_cells'}, default 'error'
         How to behave when trying to write to a sheet that already
         exists (append mode only).

pandas/io/excel/_openpyxl.py

@@ -437,12 +437,12 @@ def write_cells(
                         f"Sheet '{sheet_name}' already exists and "
                         f"if_sheet_exists is set to 'error'."
                     )
-                elif self.if_sheet_exists == "write_to":
+                elif self.if_sheet_exists == "overwrite_cells":
                     wks = self.sheets[sheet_name]
                 else:
                     raise ValueError(
                         f"'{self.if_sheet_exists}' is not valid for if_sheet_exists. "
-                        "Valid options are 'error', 'new', 'replace' and 'write_to'."
+                        "Valid options are 'error', 'new', 'replace' and 'overwrite_cells'."
                     )
             else:
                 wks = self.sheets[sheet_name]