Update Finland holidays: fix Independence Day appearing pre-1917 (#2145)

Co-authored-by: ~Jhellico <[email protected]>

holidays/countries/finland.py

@@ -28,6 +28,7 @@ class Finland(HolidayBase, ChristianHolidays, InternationalHolidays):
         - https://en.wikipedia.org/wiki/Flag_flying_days_in_Finland#Customary_flag_days
         - https://intermin.fi/en/flag-and-arms/flag-flying-days
         - https://intermin.fi/en/flag-and-arms/flag-days/2024
+        - https://en.wikipedia.org/wiki/Independence_Day_(Finland)
     """
 
     country = "FI"
@@ -90,8 +91,9 @@ def _populate_public_holidays(self):
         else:
             self._add_holiday_nov_1(name)
 
-        # Independence Day.
-        self._add_holiday_dec_6(tr("Itsenäisyyspäivä"))
+        if self._year >= 1917:
+            # Independence Day.
+            self._add_holiday_dec_6(tr("Itsenäisyyspäivä"))
 
         # Christmas Eve.
         self._add_christmas_eve(tr("Jouluaatto"))

tests/countries/test_finland.py

@@ -21,13 +21,13 @@ class TestFinland(CommonCountryTests, TestCase):
     @classmethod
     def setUpClass(cls):
         super().setUpClass(Finland)
-        cls.unofficial_holidays = Finland(categories=UNOFFICIAL, years=range(1853, 2031))
+        cls.unofficial_holidays = Finland(categories=UNOFFICIAL, years=range(1853, 2050))
 
     def test_country_aliases(self):
         self.assertAliases(Finland, FI, FIN)
 
     def test_fixed_holidays(self):
-        for year in range(2010, 2030):
+        for year in range(2010, 2050):
             self.assertHoliday(
                 f"{year}-01-01",
                 f"{year}-01-06",
@@ -167,12 +167,18 @@ def test_all_saints_day(self):
             "1957-11-01",
         )
 
+    def test_independence_day(self):
+        name = "Itsenäisyyspäivä"
+        self.assertHolidayName(name, (f"{year}-12-06" for year in range(1917, 2050)))
+        self.assertNoHoliday(f"{year}-12-06" for year in range(1853, 1917))
+        self.assertNoHolidayName(name, range(1853, 1917))
+
     def _test_unofficial_holiday(self, name, since):
         start_year, month, day = (int(part) for part in since.split("-"))
         self.assertHolidayName(
             name,
             self.unofficial_holidays,
-            (f"{year}-{month}-{day}" for year in range(start_year, 2031)),
+            (f"{year}-{month}-{day}" for year in range(start_year, 2050)),
         )
         self.assertNoHolidayName(name, self.unofficial_holidays, start_year - 1)