Why Overwriting existing commands in Cypress? - Purpose & Use Cases

The Big Idea

What if you could fix or improve all your test clicks with just one change?

The Scenario

Imagine you have many tests that use a command to click buttons, but you want to add a special check every time a button is clicked. Doing this manually means changing every test one by one.

The Problem

Manually updating each test is slow and easy to forget. You might miss some tests or introduce mistakes, making your testing unreliable and frustrating.

The Solution

Overwriting existing commands lets you change how a command works in one place. Now, every time that command runs, it includes your new behavior automatically.

Before vs After

✗ Before

cy.get('button').click(); // repeated in many tests
// manually add checks after each click

✓ After

Cypress.Commands.overwrite('click', (originalFn, subject, options) => {
  originalFn(subject, options);
  // add extra checks here
});

What It Enables

You can improve or customize common actions everywhere without touching each test, saving time and avoiding errors.

Real Life Example

For example, you can overwrite the 'click' command to always check if a loading spinner appears after clicking, ensuring your app responds correctly every time.

Key Takeaways

Manual changes to many tests are slow and error-prone.

Overwriting commands updates behavior in one place.

This makes tests easier to maintain and more reliable.

Practice

1. What is the main purpose of overwriting existing commands in Cypress?

easy

A. To change or extend the behavior of built-in Cypress commands

B. To delete commands from Cypress

C. To create new commands unrelated to existing ones

D. To speed up test execution by skipping commands

Solution

1. Step 1: Understand command overwriting

   Overwriting commands means changing how existing Cypress commands behave.

2. Step 2: Identify the purpose

   This lets you add features like logging or fix issues in commands.

3. Final Answer:

   To change or extend the behavior of built-in Cypress commands -> Option A

4. Quick Check:

   Overwriting = Change behavior [OK]

Hint: Overwriting means changing existing command behavior [OK]

Common Mistakes:

• Thinking overwriting deletes commands
• Confusing overwriting with creating new commands
• Assuming overwriting speeds up tests automatically

2. Which of the following is the correct syntax to overwrite the click command in Cypress?

easy

A. Cypress.Commands.add('click', (subject, options) => { return subject.click(options) })

B. Cypress.Commands.override('click', (originalFn, subject) => { originalFn(subject) })

C. Cypress.overwrite('click', (subject, options) => { return subject.click(options) })

D. Cypress.Commands.overwrite('click', (originalFn, subject, options) => { return originalFn(subject, options) })

Solution

1. Step 1: Recall Cypress overwrite syntax

   Use Cypress.Commands.overwrite with the command name and a function receiving originalFn.

2. Step 2: Check parameters and call

   The function must call originalFn(subject, options) to keep original behavior.

3. Final Answer:

   Cypress.Commands.overwrite('click', (originalFn, subject, options) => { return originalFn(subject, options) }) -> Option D

4. Quick Check:

   Overwrite syntax = Cypress.Commands.overwrite [OK]

Hint: Use Cypress.Commands.overwrite with originalFn first param [OK]

Common Mistakes:

• Using Cypress.Commands.add instead of overwrite
• Wrong method name like override
• Missing originalFn parameter

3. Given this overwrite code:

Cypress.Commands.overwrite('type', (originalFn, subject, text, options) => {
  cy.log(`Typing: ${text}`)
  return originalFn(subject, text, options)
})

What will happen when cy.get('input').type('hello') runs?

medium

A. It types 'hello' and logs 'Typing: hello' in the test runner

B. It types 'hello' but does not log anything

C. It throws an error because of wrong parameters

D. It logs 'Typing: hello' but does not type anything

Solution

1. Step 1: Analyze the overwrite function

   The overwrite logs the text being typed, then calls the original type command with all parameters.

2. Step 2: Understand the effect on cy.type

   When cy.get('input').type('hello') runs, it logs the message and types 'hello' into the input.

3. Final Answer:

   It types 'hello' and logs 'Typing: hello' in the test runner -> Option A

4. Quick Check:

   Overwrite logs then calls original = logs and types [OK]

Hint: Overwrite calls originalFn after logging to keep behavior [OK]

Common Mistakes:

• Assuming logging prevents typing
• Thinking parameters are incorrect
• Believing it throws an error

4. What is wrong with this overwrite code?

Cypress.Commands.overwrite('click', (subject, options) => {
  cy.log('Clicking element')
  return subject.click(options)
})

medium

A. It should use Cypress.Commands.add instead of overwrite

B. It misses the originalFn parameter required for overwriting

C. It uses cy.log which is not allowed inside overwrites

D. It calls subject.click instead of originalFn

Solution

1. Step 1: Check overwrite function parameters

   Overwrites must receive originalFn as the first parameter to call the original command.

2. Step 2: Identify missing parameter

   This code only has subject and options, missing originalFn.

3. Final Answer:

   It misses the originalFn parameter required for overwriting -> Option B

4. Quick Check:

   Overwrite needs originalFn first param [OK]

Hint: Overwrite must have originalFn as first parameter [OK]

Common Mistakes:

• Omitting originalFn parameter
• Confusing add with overwrite
• Thinking cy.log is disallowed

5. You want to overwrite the visit command to add a console log only when the URL contains 'admin'. Which overwrite code correctly implements this?

hard

A. Cypress.Commands.overwrite('visit', (url, options) => {
if (url.includes('admin')) {
console.log('Admin page visited')
}
return cy.visit(url, options)
})

B. Cypress.Commands.overwrite('visit', (originalFn, url, options) => {
if (url.includes('admin')) {
console.log('Admin page visited')
}
return originalFn(options, url)
})

C. Cypress.Commands.overwrite('visit', (originalFn, url, options) => {
if (url.includes('admin')) {
console.log('Admin page visited')
}
return originalFn(url, options)
})

D. Cypress.Commands.add('visit', (url, options) => {
if (url.includes('admin')) {
console.log('Admin page visited')
}
cy.visit(url, options)
})

Solution

1. Step 1: Use correct overwrite signature

   Overwrite must have originalFn as first parameter, then url and options.

2. Step 2: Call originalFn with correct argument order

   Call originalFn(url, options) to keep original behavior.

3. Step 3: Add conditional console log

   Check if url.includes('admin') and log message accordingly.

4. Final Answer:

   Cypress.Commands.overwrite('visit', (originalFn, url, options) => { if (url.includes('admin')) { console.log('Admin page visited') } return originalFn(url, options) }) -> Option C

5. Quick Check:

   Overwrite with originalFn and correct args [OK]

Hint: Always call originalFn with correct parameters in overwrite [OK]

Common Mistakes:

• Swapping url and options in call
• Using add instead of overwrite
• Omitting originalFn parameter