Simulate slow responses with Cypress using cy.intercept()

Today I was trying to debug a flaky test that regularly breaks our jenkins pipeline. The fault appeared to be due to a randomly slow api response.

What I usually do is that I add a delay in my server to simulate the slow response and break the test, work my way to fix it and remove the delay in the server code.

But today, I didn't have any control over the server. I had to find out another way to do that.

Turns out it's quite easy with the Cypress intercept command. You can pass a req as an argument to intercept the request, and from there use req.continue(response) to change the response.

cy.intercept(
  {
    method: 'GET',
    pathname: `_search`,
    query: {
      q: 'genera',
    },
  },
  (req) => {
    // do nothing with the req, only call the response with a 10s delay.
    req.continue((res) => {
      res.delay = 10000;
      res.send();
    });
  },
).as('practitioner');