First test for conditional requests

Involves lots of mocking. Part of the issue is that there is no way (?) to
know where repo.json is stored when blender isn't running the show.

tests/test_refresh_repos.py

@@ -0,0 +1,72 @@
+import requests
+import unittest
+from unittest import mock
+from blenderpack import fetch_repo, load_repo, write_repo
+from datetime import datetime
+import json
+
+# based on https://stackoverflow.com/a/28507806/2730823
+
+# This method will be used by the mock to replace requests.get
+def mocked_requests_get(*args, **kwargs):
+    cidict = requests.structures.CaseInsensitiveDict
+    req_headers = cidict(kwargs.get('headers'))
+    t_fmt = '%a, %m %b %Y %X %Z'
+
+    class MockResponse:
+        def __init__(self, headers: cidict, status_code: int):
+            self.headers = headers
+            self.status_code = status_code
+
+        def json(self):
+            return json.dumps({'url': 'http://someurl.tld/repo.json'})
+
+    if args[0] == 'http://someurl.tld/repo.json':
+        resp_headers = cidict({
+            "ETag": '"2a0094b-b74-55326ced274f3"',
+            "Last-Modified": 'Sun, 13 Mar 2011 13:38:53 GMT',
+        })
+
+        if req_headers == {}:
+            resp_code = 200
+        else:
+            req_headers = cidict(req_headers)
+            resp_code = 304 if req_headers.get('if-none-match', '') == resp_headers['etag']\
+                        or datetime.strptime(req_headers.get('if-modified-since', ''), t_fmt) < \
+                           datetime.strptime(resp_headers['last-modified'], t_fmt) \
+                        else 200
+        return MockResponse(resp_headers, resp_code)
+
+    return MockResponse(None, 404)
+
+_mocked_repo_storage = {}
+def mocked_load_repo(*args, **kwargs):
+    global _mocked_repo_storage
+    if args[0] not in _mocked_repo_storage:
+        _mocked_repo_storage[args[0]] = {'url': args[0]}
+
+    return _mocked_repo_storage[args[0]]
+
+def mocked_write_repo(*args, **kwargs):
+    global _mocked_repo_storage
+    _mocked_repo_storage[args[0]['url']] = args[0]
+
+
+class fetch_url_twice(unittest.TestCase):
+
+    @mock.patch('requests.get', side_effect=mocked_requests_get)
+    @mock.patch('blenderpack.load_repo', side_effect=mocked_load_repo)
+    @mock.patch('blenderpack.write_repo', side_effect=mocked_write_repo)
+    def test_fetch(self, mock_write, mock_load, mock_get):
+        fetch_repo('http://someurl.tld/repo.json')
+        mock_get.assert_called_with('http://someurl.tld/repo.json', headers={})
+
+        fetch_repo('http://someurl.tld/repo.json')
+        mock_get.assert_called_with('http://someurl.tld/repo.json', headers={
+            'If-None-Match': '"2a0094b-b74-55326ced274f3"',
+            'If-Modified-Since': 'Sun, 13 Mar 2011 13:38:53 GMT'
+            })
+
+
+if __name__ == '__main__':
+    unittest.main()