Why CSS assertions in Cypress? - Purpose & Use Cases

The Big Idea

What if your tests could spot a wrong button color faster than your eyes ever could?

The Scenario

Imagine you have a website with buttons that should be blue and text that should be bold. You open the site and check each element's style by eye, one by one, every time you make a change.

The Problem

This manual checking is slow and tiring. You might miss a color change or a font style mistake because your eyes get tired or you forget to check some parts. It's easy to make mistakes and hard to keep track of all style rules.

The Solution

CSS assertions let you write automatic tests that check if elements have the right colors, fonts, or sizes. These tests run fast and never get tired, so you catch style mistakes immediately without looking manually.

Before vs After

✗ Before

Open browser > Look at button > Guess if color is blue > Repeat for all elements

✓ After

cy.get('button').should('have.css', 'color', 'rgb(0, 0, 255)')

What It Enables

With CSS assertions, you can trust your website always looks right, even after many changes, without spending hours checking styles yourself.

Real Life Example

A designer updates the brand colors. Instead of checking every page by hand, the QA runs CSS assertion tests that quickly find any button or text still using old colors.

Key Takeaways

Manual style checks are slow and error-prone.

CSS assertions automate style verification reliably.

This saves time and ensures consistent website appearance.

Practice

1. What does the Cypress command cy.get('button').should('have.css', 'color', 'rgb(255, 0, 0)') check?

easy

A. It checks if the button is clickable.

B. It checks if the button's text color is red.

C. It checks if the button has a red background.

D. It checks if the button is visible on the page.

Solution

1. Step 1: Understand the CSS property being checked

   The command checks the CSS property 'color', which controls the text color of the element.

2. Step 2: Interpret the value 'rgb(255, 0, 0)'

   This RGB value represents the color red.

3. Final Answer:

   It checks if the button's text color is red. -> Option B

4. Quick Check:

   CSS property 'color' = text color [OK]

Hint: Check the CSS property name to know what style is tested [OK]

Common Mistakes:

• Confusing 'color' with 'background-color'
• Assuming it checks visibility instead of style
• Mixing RGB values with hex codes incorrectly

2. Which of the following is the correct Cypress syntax to assert that an element has a font size of 16 pixels?

easy

A. cy.get('p').should('css', 'font-size', '16px')

B. cy.get('p').should('have.style', 'font-size', '16px')

C. cy.get('p').assert('font-size', '16px')

D. cy.get('p').should('have.css', 'font-size', '16px')

Solution

1. Step 1: Identify the correct assertion method

   The correct Cypress assertion to check CSS is should('have.css', property, value).

2. Step 2: Match the syntax with the options

   cy.get('p').should('have.css', 'font-size', '16px') uses should('have.css', 'font-size', '16px'), which is correct syntax.

3. Final Answer:

   cy.get('p').should('have.css', 'font-size', '16px') -> Option D

4. Quick Check:

   Use should('have.css') for CSS assertions [OK]

Hint: Use 'should' with 'have.css' for CSS property checks [OK]

Common Mistakes:

• Using 'should' without 'have.css'
• Using 'assert' which is not a Cypress command
• Confusing 'have.style' with 'have.css'

3. Given the following Cypress code snippet, what will be the test result if the element's background color is actually 'rgb(0, 128, 0)'?

cy.get('.alert').should('have.css', 'background-color', 'rgb(255, 0, 0)')

medium

A. The test will fail because the background color does not match 'rgb(255, 0, 0)'.

B. The test will pass because the element has a background color.

C. The test will throw a syntax error.

D. The test will be skipped automatically.

Solution

1. Step 1: Understand the expected CSS value

   The test expects the background color to be 'rgb(255, 0, 0)', which is red.

2. Step 2: Compare with actual CSS value

   The actual background color is 'rgb(0, 128, 0)', which is green, so it does not match.

3. Final Answer:

   The test will fail because the background color does not match 'rgb(255, 0, 0)'. -> Option A

4. Quick Check:

   CSS value mismatch causes test failure [OK]

Hint: Match exact CSS values to avoid test failures [OK]

Common Mistakes:

• Assuming any color presence passes the test
• Confusing RGB values for different colors
• Expecting Cypress to auto-correct CSS mismatches

4. Identify the error in this Cypress CSS assertion and choose the fix:

cy.get('#header').should('have.css', 'font-weight', 700)

medium

A. The font-weight value should be a string: '700'.

B. The selector '#header' is invalid and should be '.header'.

C. The method 'have.css' should be replaced with 'css'.

D. The assertion should use 'expect' instead of 'should'.

Solution

1. Step 1: Check the type of CSS value in assertion

   Cypress expects the CSS value as a string, so 700 should be '700'.

2. Step 2: Verify other parts of the command

   The selector '#header' is valid, and 'should' with 'have.css' is correct syntax.

3. Final Answer:

   The font-weight value should be a string: '700'. -> Option A

4. Quick Check:

   CSS values must be strings in assertions [OK]

Hint: Always quote CSS values in Cypress assertions [OK]

Common Mistakes:

• Passing numbers instead of strings for CSS values
• Changing valid selectors unnecessarily
• Confusing assertion methods in Cypress

5. You want to verify that a button with class .submit-btn has a border radius of 5 pixels and a background color that is not transparent. Which Cypress code correctly asserts both styles?

hard

A. cy.get('.submit-btn').should('have.css', 'border-radius', '5px').and('have.css', 'background-color').not('transparent')

B. cy.get('.submit-btn').should('have.css', 'border-radius', '5px').and('have.css', 'background-color', 'rgba(0, 0, 0, 0)')

C. cy.get('.submit-btn').should('have.css', 'border-radius', '5px').and('have.css', 'background-color').should(value => expect(value).not.to.equal('rgba(0, 0, 0, 0)'))

D. cy.get('.submit-btn').should('have.css', 'border-radius', 5).and('have.css', 'background-color', 'transparent')"

Solution

1. Step 1: Assert border-radius with correct value and type

   Use should('have.css', 'border-radius', '5px') to check border radius as a string with units.

2. Step 2: Assert background-color is not transparent

   Since 'transparent' can be represented as 'rgba(0, 0, 0, 0)', use a callback assertion to check the value is not equal to that.

3. Step 3: Review options for correctness

   cy.get('.submit-btn').should('have.css', 'border-radius', '5px').and('have.css', 'background-color').should(value => expect(value).not.to.equal('rgba(0, 0, 0, 0)')) uses a callback with should and expect to verify background-color is not transparent, which is correct.

4. Final Answer:

   cy.get('.submit-btn').should('have.css', 'border-radius', '5px').and('have.css', 'background-color').should(value => expect(value).not.to.equal('rgba(0, 0, 0, 0)')) -> Option C

5. Quick Check:

   Use callback assertions for negative CSS checks [OK]

Hint: Use callback assertions to check CSS values are not equal [OK]

Common Mistakes:

• Passing numeric values without units for CSS properties
• Trying to chain 'not' directly after 'have.css' without callback
• Checking for exact transparent string instead of rgba value