How do you use cy.intercept with request and response handlers?

cy.intercept has two handler styles. A static object is a quick stub. A function handler gives you the request object, where you can inspect headers, query parameters and body, decide whether to continue to the server, and modify the response on its way back.

cy.intercept("POST", "/api/orders", (req) => {
  expect(req.body).to.have.property("items");

  req.reply((res) => {
    res.body.status = "accepted";
    res.headers["x-test"] = "true";
  });
}).as("createOrder");

cy.get("[data-cy=place-order]").click();
cy.wait("@createOrder").its("response.statusCode").should("eq", 201);

Matchers and handlers

• Use a string, glob or RegExp to match the URL
• Use a fixture option for a static response
• Use req.reply(body) to stub without calling the server
• Use req.continue() to forward the request, optionally modifying it
• Use req.on with a response event to observe or alter the real response
• Use a route matcher function for complex matching, such as request body fields

The request body is only available once Cypress has parsed it. For a POST, the body is usually an object; for some content types it may be a string. Do not assume a shape without checking the request, and avoid mutating a request in a way that changes the behaviour under test.