In cypress, how do I wait for a page to load?

You can add some assert inside:

cy.click('#someButtonToNavigateOnNewPage');

cy.location('pathname', {timeout: 60000})
  .should('include', '/newPage');

cy.click('#YouAreOnNewPage');

You can change default timeout – by default it’s 4000 ms (4 secs) – to ensure that user navigated the page. I’ve put a big number here – 60,000 ms – because I’m sure that 99% of users will leave if they do not have page loaded after 1 min.