Adding end-to-end tests

The first test is testing a tricky cache scenario with the back when testing variables.
The end-to-end package used is testcafe.

tests/README.md

@@ -0,0 +1,18 @@
+End-to-end tests
+
+This directory contains automated end to end tests.
+
+To run them locally:
+
+```console
+$ npm install
+$ npm test
+```
+
+Alternatively, you can use docker-compose to run the tests:
+
+```console
+$ docker-compose -f docker-compose.testcafe.yml up
+```
+
+Note: by default, tests are running in Chrome locally and in Chromium in the Docker image.