added some tests for save_api interface

tests/test_save_api.py

@@ -0,0 +1,20 @@
+import pytest
+import time
+from datetime import datetime
+
+from waybackpy.save_api import WaybackMachineSaveAPI
+
+
+def test_save():
+    url = "https://github.com/akamhy/waybackpy"
+    user_agent = "Mozilla/5.0 (MacBook Air; M1 Mac OS X 11_4) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.1.1 Safari/604.1"
+    save_api = WaybackMachineSaveAPI(url, user_agent)
+    save_api.save()
+    archive_url = save_api.archive_url
+    timestamp = save_api.timestamp()
+    headers = save_api.headers  # CaseInsensitiveDict
+    cached_save = save_api.cached_save
+    assert cached_save in [True, False]
+    assert archive_url.find("github.com/akamhy/waybackpy") != -1
+    assert str(headers).find("github.com/akamhy/waybackpy") != -1
+    assert type(save_api.timestamp()) == type(datetime(year=2020, month=10, day=2))