Missing exception when using cy.log() in Promise: Instead return value is modified

[gabbersepp]

Current behavior:

When cy.xx is called inside a Promise that returns something, no exception is thrown. Instead, the return value is modified to be the return value of the cy.xxx call.

Desired behavior:

I know that we are not allowed to call cy.xxx commands within promises. But it is very confusing to modify the return value instead throwing an exception.
In our case we used cy.log() and were wondering why we receive "undefined".
I would expect an exception to be thrown.

Steps to reproduce:

 function makeSomething(log: boolean): void {
  cy
    .then(() => Promise.resolve().then(() => returnTrue(log)))
    .then((val: boolean) => cy.log(`val is: ${val}`))
    .wait(5000);
}

function returnTrue(log: boolean): boolean {
  if (log) {
    cy.log("Test");
  }

  return true;
}

describe("Test", () => {
  it("test with log", () => {
    makeSomething(true);
  });

  it("test without log", () => {
    makeSomething(false);
  });
});

Output:

test with log
LOG val is: null
test without log
LOG val is: true

Versions

Cypress 3.1.5
Windows 10
Chrome 72.0.3626.109 (Official Build) (64-Bit)

[BiosBoy]

Same here. Any updates?

[jennifer-shehane]

This is because cy.log() yields null which is what the Promise resolves to. If you changed the cy.log() line to cy.window() - you would see that the yield of the Cypress command (<window>) is being passed on to the next .then().

And yes, this is why we advise against running cypress commands within Promises since commands themselves are promises and it's confusing if you mix Promise chains within Promise chains.

We try to throw a warning in these cases, but I suppose this is an instance where we don't.

Simplified version of what is happening.

it("test with log", () => {
  cy.then(() => {
      return Promise.resolve().then(() => {
        // THIS LINE IS DIFFERENT
        cy.log("Test") // enqueued, then runs

        return true
      })
    })
    .then((val) => {
      expect(val).to.be.true
    })
})

it("test without log", () => {
  cy.then(() => {
      return Promise.resolve().then(() => {
        return true
      })
    })
    .then((val) => {
      expect(val).to.be.true
    })
});