pythongh-57539: Add tests for LocaleTextCalendar.formatweekday

This patch has already been applied to `main` branch (via pythongh-93468), but
with wrong copyright. After merging this commit to `main`, git `Author`
metadata will be updated to the original author.

Lib/test/test_calendar.py

@@ -605,6 +605,16 @@ def test_locale_calendars(self):
  new_october = calendar.TextCalendar().formatmonthname(2010, 10, 10)
  self.assertEqual(old_october, new_october)
 
+ def test_locale_calendar_formatweekday(self):
+ # formatweekday uses different day names based on the available width.
+ cal = calendar.LocaleTextCalendar(locale='en_US')
+ # For short widths, a centered, abbreviated name is used.
+ self.assertEqual(cal.formatweekday(0, 5), " Mon ")
+ # For really short widths, even the abbreviated name is truncated.
+ self.assertEqual(cal.formatweekday(0, 2), "Mo")
+ # For long widths, the full day name is used.
+ self.assertEqual(cal.formatweekday(0, 10), " Monday ")
+
  def test_locale_html_calendar_custom_css_class_month_name(self):
  try:
  cal = calendar.LocaleHTMLCalendar(locale='')