Add tests for two_digit_year_to_four_digit_year

tests/test_model/test_reftek/test_gps.py

+import unittest
+
+from sohstationviewer.model.reftek.reftek import (
+    two_digit_year_to_four_digit_year
+)
+
+
+class TestTwoDigitYearToFourDigitYear(unittest.TestCase):
+    def test_2000_years(self):
+        test_cases = {
+            '0': '2000',
+            '00': '2000',
+            '1': '2001',
+            '01': '2001',
+            '12': '2012',
+            '68': '2068',
+        }
+        for input, expected_output in test_cases.items():
+            with self.subTest(f'test_input_{input}'):
+                result = two_digit_year_to_four_digit_year(input)
+                self.assertEqual(result, expected_output)
+
+    def test_1900_years(self):
+        test_cases = {
+            '69': '1969',
+            '99': '1999',
+            '75': '1975',
+        }
+        for input, expected_output in test_cases.items():
+            with self.subTest(f'test_input_{input}'):
+                result = two_digit_year_to_four_digit_year(input)
+                self.assertEqual(result, expected_output)
+
+    def test_invalid_input(self):
+        with self.subTest('test_negative_year'):
+            input = '-1'
+            with self.assertRaises(ValueError):
+                two_digit_year_to_four_digit_year(input)
+        with self.subTest('test_year_has_more_than_two_dgit'):
+            input = '123'
+            with self.assertRaises(ValueError):
+                two_digit_year_to_four_digit_year(input)
+        with self.subTest('test_non_sensical_input'):
+            input = 'tt'
+            with self.assertRaises(ValueError):
+                two_digit_year_to_four_digit_year(input)
+