Fixed Thai Calendar test case coverage (#2090)

tests/test_holiday_groups.py

@@ -12,7 +12,8 @@
 
 from unittest import TestCase
 
-from holidays.groups import ChristianHolidays, InternationalHolidays
+from holidays.calendars.thai import KHMER_CALENDAR
+from holidays.groups import ChristianHolidays, InternationalHolidays, ThaiCalendarHolidays
 from holidays.holiday_base import HolidayBase
 
 
@@ -57,3 +58,30 @@ def __init__(self, *args, **kwargs):
             ValueError,
             lambda: test_holidays._add_childrens_day("Invalid", "INVALID_TYPE"),
         )
+
+
+class TestThaiCalendarHolidays(TestCase):
+    def test_add_thai_calendar_holiday(self):
+        # Check for out-of-range dates.
+        class TestHolidays(HolidayBase, ThaiCalendarHolidays):
+            def __init__(self, *args, **kwargs):
+                ThaiCalendarHolidays.__init__(self)
+                super().__init__(*args, **kwargs)
+
+        test_holidays = TestHolidays()
+
+        test_holidays._populate(2158)
+        test_holidays._add_asarnha_bucha("Asarnha Bucha")
+        test_holidays._add_boun_haw_khao_padapdin("Boun Haw Khao Padapdin")
+        test_holidays._add_boun_haw_khao_salark("Boun Haw Khao Salark")
+        test_holidays._add_boun_suang_heua("Boun Suang Huea")
+        test_holidays._add_khao_phansa("Khao Phansa")
+        test_holidays._add_loy_krathong("Loy Krathong")
+        test_holidays._add_makha_bucha("Makha Bucha")
+        test_holidays._add_makha_bucha("Meak Bochea", KHMER_CALENDAR)
+        test_holidays._add_ok_phansa("Ok Phansa")
+        test_holidays._add_pchum_ben("Pchum Ben")
+        test_holidays._add_preah_neangkoal("Royal Ploughing Ceremony (Cambodia)")
+        test_holidays._add_visakha_bucha("Visakha Bucha")
+        test_holidays._add_visakha_bucha("Visaka Bochea", KHMER_CALENDAR)
+        self.assertEqual(0, len(test_holidays))