allow sending params in transmission list endpoint

sparkpost/transmissions.py

@@ -265,15 +265,17 @@ def get(self, transmission_id):
         results = self._fetch_get(transmission_id)
         return results['transmission']
 
-    def list(self):
+    def list(self, **kwargs):
         """
         Get a list of your transmissions
 
+        :param campaign_id: ID of the campaign used by the transmissions
+        :param template_id: ID of the template used by the transmissions
+
         :returns: list of transmissions
         :raises: :exc:`SparkPostAPIException` if API call fails
         """
-        results = self.request('GET', self.uri)
-        return results
+        return self.request('GET', self.uri, params=kwargs)
 
     def delete(self, transmission_id):
         """

test/test_transmissions.py

@@ -310,6 +310,22 @@ def test_success_list():
     assert response == []
 
 
+@responses.activate
+def test_success_list_with_params():
+    responses.add(
+        responses.GET,
+        'https://api.sparkpost.com/api/v1/transmissions?template_id=abcd',
+        status=200,
+        content_type='application/json',
+        body='{"results": []}',
+        match_querystring=True
+
+    )
+    sp = SparkPost('fake-key')
+    response = sp.transmission.list(template_id='abcd')
+    assert response == []
+
+
 @responses.activate
 def test_success_delete():
     responses.add(