Add unit test for environment variable HAPROXY templates

tests/test_marathon_lb.py

@@ -98,6 +98,38 @@ def test_config_no_apps(self):
   bind *:9091
   mode http
 
+frontend marathon_https_in
+  bind *:443 ssl crt /etc/ssl/cert.pem
+  mode http
+'''
+        print("actual config:\n")
+        print(config)
+        self.assertMultiLineEqual(config, expected)
+
+    def test_config_env_template(self):
+        apps = dict()
+        groups = ['external']
+        bind_http_https = True
+        ssl_certs = ""
+        os.environ["HAPROXY_HTTP_FRONTEND_HEAD"] = '''
+frontend changed_frontend
+  bind *:80
+  mode http
+        '''
+        templater = marathon_lb.ConfigTemplater()
+        del os.environ["HAPROXY_HTTP_FRONTEND_HEAD"]
+
+        config = marathon_lb.config(apps, groups, bind_http_https,
+                                    ssl_certs, templater)
+        expected = self.base_config + '''
+frontend changed_frontend
+  bind *:80
+  mode http
+
+frontend marathon_http_appid_in
+  bind *:9091
+  mode http
+
 frontend marathon_https_in
   bind *:443 ssl crt /etc/ssl/cert.pem
   mode http