To take a screenshot on failure where we have our common error
handling code in common.run_test method we need to have access to
the Page instance. Currently, we create a new Page in the test method
we pass into run_test, so we pass in a new Page instance to that method
so the test and the run_test method have access to the same Page. And,
then we take a screenshot on failure. It will be saved as `failure-${num}`
in var/puppeteer directory.
In common.js, we now have a single browser instance for the whole
test. When we update the test-js-with-puppetter to spawn a single
node process, like we do for node tests, we will save time on having
to open an new browser for every test + puppetter start up cost.
We will also add some more helpers here like a method for
filling out a form easily etc.
