Wait for async method in for loop in Cypress

Question

Edit: Why this is not a duplicate: because Cypress, just read instead of tagging everything as duplicate.

Edit 2: Also, see answer for better understanding of the differences between usual async for loops problems and this question.

I am writing cypress tests and I want to create a cypress command that populates my database with a list of users. I want the creation loop to wait for each user to be created before it moves on to the next one (because I want that done in a specific order).

For now, my loop looks like this:

Cypress.Commands.add("populateDb", (users) => {
  var createdItems = []

  for (const user of users) {
    cy.createUser(user, 'passe').then(response => {
      createdUsers.unshift(response.body.user)
    })
  }
  return createdItems
})

Of course, this loop does not wait for each user to be created before moving onto the next one (I want 'sequential treatment', NOT 'parallel and then wait for all promise to resolve')

I have read the answers about async for-loop here:

But I can't seem to find what I want, mainly because cypress wont allow me to declare my function as async as follow :

Cypress.Commands.add("populateDb", async (users) => {
    //Some code
})

And If I don't declare it async I am not able to use await.

Isn't there some king of get() method that just synchronously wait for a Promise to resolve?

score 2 · Answer 1 · answered Jul 27 '20 at 13:49

Using a combination of wrap and each cypress command I was able to achieve a loop that waits for each iteration and can return the full results without needing a global variable.

The only reason I use the wrap command is because the cypress command each requires it to be chained off a previous cypress command. The each command will evaluate each iteration and finally call the then where you can return the complete results array. I am using this to upload multiple files and return the list of keys, but you can modify this for your own need.

Cypress.Commands.add("uploadMultipleFiles", (files) => {
    var uploadedS3Keys = []
    cy.wrap(files).each((file, index, list) => {
        cy.uploadFileToOrdersApi(file)
            .then(s3Key => uploadedS3Keys.push(s3Key))
    }).then(() => uploadedS3Keys)
})

Tom · Accepted Answer · 2018-10-12T12:46:26.933

Turns out there is a reason why cypress is so restrictive about what you can do about waiting for async method to resolve: it always automatically runs all the async commands in sequential order, as they are called, not in parallel, so this will execute in the right order even if createUser is Async :

Cypress.Commands.add("populateDb", (users) => {
  for (const user in users) {
    cy.createUser(user).then(response => {
      console.log(response)
    })
  }
})

If you want to get the value of what is returned (in my case, I need the user ID to delete them later), you can just store them in a var at file root level and add a cypress command that returns that var.

var createdItems = []

Cypress.Commands.add("getCreatedItems", () => {
  return createdItems
})

Cypress.Commands.add("populateDb", (users) => {
  for (const user in users) {
    cy.createUser(user).then(response => {
      createdItems.unshift(response) // I unshift() because I need to delete them in FILO order later
    })
  }
})

Then in the cypress test file you can just call them in the order you need them to execute :

cy.populateDb(users)
cy.getCreatedItems().then(response => {
  //response is my createdItems Array, and cy.getCreatedItems() will run only when cy.populateDb() is resolved
})

Mikael Lepistö · Answer 3 · 2019-10-03T07:45:13.070

You could do it also like:

Cypress.Commands.add("populateDb", (users) => {
  for (const user in users) {
    cy.createUser(user).then(response => {
      createdItems.unshift(response) // I unshift() because I need to delete them in FILO order later
    })
  }

  return createdItems;
})

cy.populateDb(users).then(response => {
  // ... runs after populate ...
})

But the other answer is also right. Each cy.xxxxx command is actually added to command queue and ran one after each other. If during queue execution new cy.xxxxx2 commands are called, they will be added to front of the queue.

Here is simple example to explain the execution order of cypress command queue and synchronous code:

const a = 1; // a == 1

cy.cmd1().then(() => {
  cy.cmd2().then(() => {
    a += 1; // a == 5
  });

  a += 1; // a == 3

  cy.cmd3()
  a += 1; // a == 4
});

cy.cmd4().then(() => {
  a += 1; // a == 6
});

a += 1; // a == 2

// at this point cypress command queue starts running the queue that is cmd1, cmd4

// 1. cmd1 runs and adds cmd2 and cmd3 to front of command queue also adds +2 to a
// 2. cmd2 runs and adds +1 to a
// 3. cmd3 runs
// 4. cmd4 runs and adds +1 to a
// ... all done ...

So from this example you can see that in your case you loop will be executed serially, because each cy.createUser is added to cypress command queue and executed then sequentially.

Wait for async method in for loop in Cypress

3 Answers3