test(sequence): add Stellar account sequence monotonic increment specs

tests/wave14_account_sequence_increment_test.py

@@ -0,0 +1,22 @@
+import unittest
+
+class TestWave14AccountSequenceIncrement(unittest.TestCase):
+    def test_stellar_sequence_monotonic_increment(self):
+        def get_next_sequence_number(current_seq: int) -> int:
+            return current_seq + 1
+
+        initial_seq = 123456789012345
+        next_seq = get_next_sequence_number(initial_seq)
+        self.assertEqual(next_seq, 123456789012346)
+        self.assertTrue(next_seq > initial_seq)
+
+    def test_sequence_number_positive_int64(self):
+        def is_valid_sequence(seq: int) -> bool:
+            return seq > 0 and seq <= (1 << 63) - 1
+
+        self.assertTrue(is_valid_sequence(100))
+        self.assertFalse(is_valid_sequence(0))
+        self.assertFalse(is_valid_sequence(-50))
+
+if __name__ == '__main__':
+    unittest.main()