Fixed description argument for create_from_mirror

* Fixed Snapshot.create_from_mirror. Description argument was not being
  set in the post.
* Fixed test_create_from_mirror to check the post request fields to make
  sure they match expected values.

Author: Greg Land

aptly_api/parts/snapshots.py

@@ -56,6 +56,9 @@ def create_from_mirror(self, mirrorname: str, snapshotname: str, description: Op
         body = {
             "Name": snapshotname
         }
+        if description is not None:
+            body["Description"] = description
+
         resp = self.do_post("api/mirrors/%s/snapshots" %
                             quote(mirrorname), json=body)
         return self.snapshot_from_response(resp.json())

aptly_api/tests/test_snapshots.py

@@ -207,6 +207,7 @@ def test_create_from_packages(self, *, rmock: requests_mock.Mocker) -> None:
         )
 
     def test_create_from_mirror(self, *, rmock: requests_mock.Mocker) -> None:
+        expected = {'Name': 'aptly-mirror-snap', 'Description': 'Snapshot from local repo [aptly-repo]'}
         rmock.post("http://test/api/mirrors/aptly-mirror/snapshots",
                    text='{"Name":"aptly-mirror-snap","CreatedAt":"2022-11-29T21:43:45.275605639Z",'
                         '"Description":"Snapshot from local mirror [aptly-mirror]"}')
@@ -219,3 +220,4 @@ def test_create_from_mirror(self, *, rmock: requests_mock.Mocker) -> None:
                 created_at=iso8601.parse_date('2022-11-29T21:43:45.275605639Z')
             )
         )
+        self.assertEqual(rmock.request_history[0].json(), expected)