Add tests for portfolio funding route

This adds a helper to grab a template's context. Using a helper from the
Flask documentation: http://flask.pocoo.org/docs/1.0/signals/?highlight=template_rendered#subscribing-to-signals

tests/utils.py

@@ -0,0 +1,16 @@
+from flask import template_rendered
+from contextlib import contextmanager
+
+
+@contextmanager
+def captured_templates(app):
+    recorded = []
+
+    def record(sender, template, context, **extra):
+        recorded.append((template, context))
+
+    template_rendered.connect(record, app)
+    try:
+        yield recorded
+    finally:
+        template_rendered.disconnect(record, app)