Wait for an own function (which returns a promise) before tests are executed

You can use cy.wrap( promise ), although there might still be a bug where it never times out (haven't tested).

Otherwise, you can use cy.then() (which is undocumented, can break in the future, and I'm def not doing any favors by promoting internal APIs):

cy.then(() => {
    return myAsyncFunction();
});

You can use both of these commands at the top-level of spec like you'd use any command and it'll be enqueued into cypress command queue and executed in order.

But unlike cy.wrap (IIRC), cy.then() supports passing a callback, which means you can execute your async function at the time of the cy command being executed, not at the start of the spec (because expressions passed to cy commands evaluate immediately) --- that's what I'm doing in the example above.

Cypress have promises (Cypress.Promise), but they are not real promises, more like duck typing. In fact, Cypress isn't 100% compatible with real promises, they might, or might not, work.

Think of Cypress.Promise as a Task or an Action. They are executed sequentially with all other cypress commands.

To get your function into the Cypress pipeline you can use custom commands. The documentation doesn't state it, but you can return a Cypress.Promise from them.

Cypress.Commands.add('resetDb', function () {
  var apiServerUrl = Cypress.config().apiServerUrl;
  return new Cypress.Promise((resolve, reject) => {
    httpRequest('PUT', apiServerUrl + "/api/test/reset/")
      .then(function (data) {
        resolve();
      })
      .catch(function (err) {
        reject(err);
      });
  });
});

That command can then be executed from the test itself, or as in my case from before().

describe('Account', function () {
  before(() => {
    cy.resetDb();
  });

  it('can login', function () {
    // test code
  });

})