cy.wait(#someXhr) taimeouts - cypress

Question

I'm having a problem with stubbing a simple request to an API using the cypress' cy.server() and cy.route().
Here's the failing test:
it.only("should show an error message for server errors", () => {
const name = "It doesnt matter";
const email = "takenemail#yopmail.com";
const pass = "123123";
// run the server and define the stubbed route
cy.server();
cy.route(
"POST",
`${serverBaseUrl}/auth/register`,
"fixture:register-fail.json"
).as("postRegister");
// fill in the registration form and hit submit
cy.visit("/auth/register");
cy.get(selectors.registerForm.name).type(name);
cy.get(selectors.registerForm.email).type(email);
cy.get(selectors.registerForm.password).type(pass);
cy.get(selectors.registerForm.registerButton).click();
// intercept the request and mock it
cy.wait("#postRegister"); // this fails.
cy.get(selectors.registerForm.genericErrors).contains(
"This email has already been taken"
);
});
and the error:
cy.wait() timed out waiting 5000ms for the 1st request to the route: postRegister. No request ever occurred.
Note: even though it says that No request ever occurred. I can still see the request being send and a response received in the console's Network tab (which means the stub has been bypassed and a regular request's been made).
Any ideas what's happening?
Thanks in advance.

Answer 1

Ok, seems like i have found the problem.
It turns out that using the fetch API is not supported by cypress.
The workaround - using whatwg-fetch, which is basically a polyfill for the fetch api, working with XHR behind the scenes.
Install the whatwg-fetch package: npm install whatwg-fetch --save
Import it in your project: import "whatwg-fetch";
Last, but very important - remove the fetch object from the window before every page load in the cypress environment like this:
// you can define this in the commands file for example...
Cypress.on("window:before:load", (win) => delete win.fetch);
or an alternative, per-visit approach:
it("some test", () => {
cy.visit("/url", {
onBeforeLoad: win => delete win.fetch // <---
});
// ...the rest of the test
});
Doing this will kick-in the polyfill and the stubbing should be working properly after this intervention.