The Grouparoo Blog

Testing storage with Selenium (Node)

Tagged in Engineering Notes 
By Sean C Davis on 2021-02-18

We have a feature on this site that is using sessionStorage to send analytics data we want to capture. Being that it's an important feature, we should write test(s) to cover the use case(s), right?

Okay, fine. Let's do it!

This website is a Next.js application that uses Jest as our test runner and Selenium WebDriver for integration test help.

What I wanted to do with Jest and Selenium was to read from sessionStorage after visiting a series of pages. After a bit of perusing, I finally uncovered a (goofy) way to achieve what I wanted.

We can use the executeScript method to run a JavaScript expression and capture the result. Our test looks like this:

declare var browser: any;

async function getSessionItem(key) {
  return await browser.executeScript(
    `return window.sessionStorage.getItem("${key}");`

test("stores page history in the session data", async () => {
  await browser.get(url + `/docs/config`);
  expect(await getSessionItem("prevPath")).toBe("null");
  expect(await getSessionItem("currentPath")).toBe("/docs/config");
  await browser.get(url + `/meet`);
  expect(await getSessionItem("prevPath")).toBe("/docs/config");
  expect(await getSessionItem("currentPath")).toBe("/meet");

Here are a few of the key items to note:

  • You must return the JavaScript expression or you'll end up with undefined.
  • It's a much cleaner approach to run tests as async functions so you can use await to retrieve the result of the script, rather than ending up in a nightmarish Promise chain.
  • browser is often referred to as driver in other documentation and implementations. This comes from the library we're using to connect Jest and Selenium.

This now works like a charm! You could take a similar approach if you wanted to read from any other JavaScript object, including localStorage.

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