Adding test of file uploading.

Author: jasedit

tests/data/slack_logo.png

@@ -1,6 +1,21 @@
 from slackclient._slackrequest import SlackRequest
 import json
+import os
 
+def test_post_file(mocker):
+    requests = mocker.patch('slackclient._slackrequest.requests')
+
+    response = SlackRequest.do('xoxb-123',
+        'files.upload',
+        {'file': open(os.path.join('.', 'tests', 'data', 'slack_logo.png'), 'rb'),
+            'filename': 'slack_logo.png'})
+
+    assert requests.post.call_count == 1
+    args, kwargs = requests.post.call_args
+    assert 'https://slack.com/api/files.upload' == args[0]
+    assert {'filename': 'slack_logo.png',
+            'token': 'xoxb-123'} == kwargs['data']
+    assert None != kwargs['files']
 
 def test_post_attachements(mocker):
     requests = mocker.patch('slackclient._slackrequest.requests')