Update sdkVersion in graph_session.py

Fixes #42

Prepended sdkVersion with comma separated new values in self.headers in graph_session.py
Modified a test and added another test to check whether the value has been updated correctly

Author: rajatdiptabiswas

msgraphcore/graph_session.py

@@ -20,7 +20,11 @@ class GraphSession(Session):
     """
     def __init__(self, auth_provider: AuthProviderBase, middleware: list = []):
         super().__init__()
-        self.headers.update({'sdkVersion': 'graph-python-' + SDK_VERSION})
+        if 'sdkVersion' not in self.headers:
+            self.headers.update({'sdkVersion': 'graph-python-' + SDK_VERSION})
+        else:
+            self.headers.update({'sdkVersion': 'graph-python-' + SDK_VERSION + ', '
+                                               + self.headers.get('sdkVersion')})
         self._base_url = BASE_URL
 
         auth_handler = AuthorizationHandler(auth_provider)

tests/unit/test_graph_session.py

@@ -24,7 +24,11 @@ def test_has_graph_url_as_base_url(self):
         self.assertEqual(self.requests._base_url, BASE_URL)
 
     def test_has_sdk_version_header(self):
-        self.assertEqual(self.requests.headers.get('sdkVersion'), 'graph-python-'+SDK_VERSION)
+        self.assertTrue('sdkVersion' in self.requests.headers)
+
+    def test_updated_sdk_version(self):
+        self.assertTrue(self.requests.headers.get('sdkVersion')
+                        .startswith('graph-python-'+SDK_VERSION))
 
     def test_initialized_with_middlewares(self):
         graph_session = GraphSession(self.auth_provider)