Dynamic response stubbing in Cypress - Framework Patterns

Framework Mode - Dynamic response stubbing

Folder Structure

    cypress/
    ├── e2e/                  # Test specs
    │   └── dynamicStub.cy.js # Tests using dynamic response stubbing
    ├── fixtures/             # Static test data
    │   └── example.json
    ├── support/              # Custom commands and utilities
    │   ├── commands.js       # Custom Cypress commands
    │   └── index.js          # Support file loaded before tests
    ├── plugins/              # Plugins for Cypress (optional)
    └── cypress.config.js     # Cypress configuration file
    

Test Framework Layers

• Test Specs (e2e/): Contains test files that define test cases using dynamic stubbing with cy.intercept().
• Fixtures (fixtures/): Holds static JSON or other data files used to stub responses when needed.
• Support (support/): Contains reusable commands and utilities, such as custom commands to simplify dynamic stubbing logic.
• Configuration (cypress.config.js): Defines environment variables, base URLs, and browser settings.

Configuration Patterns

Use cypress.config.js to manage environments and base URLs:

import { defineConfig } from 'cypress';

export default defineConfig({
  e2e: {
    baseUrl: 'https://example.com',
    env: {
      apiUrl: 'https://api.example.com',
      userToken: 'test-token'
    },
    setupNodeEvents(on, config) {
      // plugins can be added here
    }
  }
})
    

In tests, access environment variables with Cypress.env() to dynamically stub responses based on environment or test data.

Test Reporting and CI/CD Integration

• Use built-in Cypress reporter or integrate with mochawesome for detailed HTML reports.
• Configure CI pipelines (GitHub Actions, Jenkins, GitLab CI) to run Cypress tests headlessly with cypress run.
• Store test artifacts like screenshots and videos for failed tests to help debugging dynamic stubbing issues.
• Use environment variables in CI to switch API endpoints or stub data dynamically.

Best Practices for Dynamic Response Stubbing

1. Use cy.intercept() with functions to dynamically modify responses based on request data or test state.
2. Keep stub logic in support commands to reuse dynamic stubbing patterns and keep tests clean.
3. Use fixtures for static parts of stubbed responses and merge dynamically generated data as needed.
4. Isolate tests by resetting stubs before each test to avoid cross-test interference.
5. Log intercepted requests and responses during test runs to help debug dynamic stubbing behavior.

Self Check

Where in this folder structure would you add a reusable custom command to simplify dynamic response stubbing?

Key Result

Organize Cypress tests with clear folder layers and use cy.intercept() with dynamic logic for flexible response stubbing.

Practice

1. What is the main purpose of dynamic response stubbing in Cypress tests?

easy

A. To change server responses during tests to simulate different scenarios

B. To speed up the browser rendering process

C. To automatically generate test data from the server

D. To record user interactions for playback

Solution

1. Step 1: Understand dynamic response stubbing

   Dynamic response stubbing allows tests to modify server replies on the fly to simulate various conditions.

2. Step 2: Identify the main goal

   This helps test how the app behaves with different data or errors without relying on real server responses.

3. Final Answer:

   To change server responses during tests to simulate different scenarios -> Option A

4. Quick Check:

   Dynamic stubbing = simulate different server replies [OK]

Hint: Dynamic stubbing means changing server replies during tests [OK]

Common Mistakes:

• Confusing stubbing with speeding up rendering
• Thinking it generates test data automatically
• Mixing it up with recording user actions

2. Which of the following is the correct way to stub a dynamic response using cy.intercept in Cypress?

easy

A. cy.intercept('GET', '/api/data', { status: 200, body: { value: 42 } })

B. cy.intercept('GET', '/api/data', (res) => { res.send({ value: 42 }) })

C. cy.intercept('GET', '/api/data', () => { return { value: 42 } })

D. cy.intercept('GET', '/api/data', (req) => { req.reply({ body: { value: 42 } }) })

Solution

1. Step 1: Recall cy.intercept syntax for dynamic stubbing

   To modify the response dynamically, use a callback with the request object and call req.reply() with the new body.

2. Step 2: Check each option

   cy.intercept('GET', '/api/data', (req) => { req.reply({ body: { value: 42 } }) }) correctly uses (req) => { req.reply({ body: ... }) }. cy.intercept('GET', '/api/data', { status: 200, body: { value: 42 } }) is static stubbing, C returns a value incorrectly, D uses res.send which is not Cypress syntax.

3. Final Answer:

   cy.intercept('GET', '/api/data', (req) => { req.reply({ body: { value: 42 } }) }) -> Option D

4. Quick Check:

   Dynamic stub uses req.reply() callback [OK]

Hint: Use req.reply() inside intercept callback for dynamic response [OK]

Common Mistakes:

• Using static object instead of callback for dynamic stubbing
• Returning response instead of calling req.reply()
• Using incorrect callback parameter names

3. Given the following Cypress code, what will be the response body when the app requests '/api/user'?

cy.intercept('GET', '/api/user', (req) => {
  const id = req.query.id
  if (id === '1') {
    req.reply({ body: { name: 'Alice' } })
  } else {
    req.reply({ body: { name: 'Guest' } })
  }
})

The app calls fetch('/api/user?id=1'). What is the response?

medium

A. Empty response body

B. { name: 'Guest' }

C. { name: 'Alice' }

D. An error occurs because req.query is undefined

Solution

1. Step 1: Analyze the intercept callback logic

   The callback checks req.query.id. If it equals '1', it replies with { name: 'Alice' }, else { name: 'Guest' }.

2. Step 2: Check the request URL query

   The app calls '/api/user?id=1', so req.query.id is '1'. Therefore, the response is { name: 'Alice' }.

3. Final Answer:

   { name: 'Alice' } -> Option C

4. Quick Check:

   Query id '1' returns Alice [OK]

Hint: Match query params in req.query to decide response [OK]

Common Mistakes:

• Assuming req.query is undefined in Cypress intercept
• Ignoring query parameters in the stub
• Confusing string and number types in comparison

4. Identify the error in this Cypress dynamic stub code:

cy.intercept('POST', '/api/login', (req) => {
  req.reply({ statusCode: 200, body: { token: 'abc123' } })
})

The test fails with an error about req.reply not being a function. What is wrong?

medium

A. The callback receives req but req.reply is not a function; should use req.continue

B. The callback parameter should be interception and interception.reply used

C. The callback parameter is correct, but req.reply is only available on res

D. The callback parameter should be named res instead of req

Solution

1. Step 1: Understand intercept callback parameter

   The callback receives an interception object, often named interception, which has the reply method.

2. Step 2: Identify the naming and usage error

   Using req as parameter is allowed but req.reply is not a function because the object is not the request but the interception. The correct approach is to name it interception and call interception.reply().

3. Final Answer:

   The callback parameter should be interception and interception.reply used -> Option B

4. Quick Check:

   Use interception.reply() in intercept callback [OK]

Hint: Use interception.reply(), not req.reply(), in intercept callback [OK]

Common Mistakes:

• Confusing request object with interception object
• Using req.reply() which does not exist
• Misnaming callback parameter causing method errors

5. You want to stub a GET request to '/api/items' so that the response body depends on a query parameter 'type'. If 'type' is 'fruit', respond with { items: ['apple', 'banana'] }. If 'type' is 'vegetable', respond with { items: ['carrot', 'lettuce'] }. Otherwise, respond with { items: [] }. Which code correctly implements this dynamic response stubbing?

hard

A. cy.intercept('GET', '/api/items', (interception) => {
const type = interception.query.type
if (type === 'fruit') {
interception.reply({ body: { items: ['apple', 'banana'] } })
} else if (type === 'vegetable') {
interception.reply({ body: { items: ['carrot', 'lettuce'] } })
} else {
interception.reply({ body: { items: [] } })
}
})

B. cy.intercept('GET', '/api/items', (req) => {
if (req.query.type === 'fruit') {
req.reply({ items: ['apple', 'banana'] })
} else if (req.query.type === 'vegetable') {
req.reply({ items: ['carrot', 'lettuce'] })
} else {
req.reply({ items: [] })
}
})

C. cy.intercept('GET', '/api/items', (req) => {
const type = req.query.type
if (type === 'fruit') {
req.reply({ body: { items: ['apple', 'banana'] } })
} else if (type === 'vegetable') {
req.reply({ body: { items: ['carrot', 'lettuce'] } })
} else {
req.reply({ body: { items: [] } })
}
})

D. cy.intercept('GET', '/api/items', (interception) => {
const type = interception.query.type
if (type === 'fruit') {
interception.send({ body: { items: ['apple', 'banana'] } })
} else if (type === 'vegetable') {
interception.send({ body: { items: ['carrot', 'lettuce'] } })
} else {
interception.send({ body: { items: [] } })
}
})

Solution

1. Step 1: Identify correct parameter and method usage

   The callback parameter should be named interception (or similar) and use interception.reply() to send the response with a body property.

2. Step 2: Check each option for correctness

   cy.intercept('GET', '/api/items', (interception) => { const type = interception.query.type if (type === 'fruit') { interception.reply({ body: { items: ['apple', 'banana'] } }) } else if (type === 'vegetable') { interception.reply({ body: { items: ['carrot', 'lettuce'] } }) } else { interception.reply({ body: { items: [] } }) } }) correctly uses interception.query.type and calls interception.reply({ body: ... }). cy.intercept('GET', '/api/items', (req) => { if (req.query.type === 'fruit') { req.reply({ items: ['apple', 'banana'] }) } else if (req.query.type === 'vegetable') { req.reply({ items: ['carrot', 'lettuce'] }) } else { req.reply({ items: [] }) } }) misses body wrapper. cy.intercept('GET', '/api/items', (req) => { const type = req.query.type if (type === 'fruit') { req.reply({ body: { items: ['apple', 'banana'] } }) } else if (type === 'vegetable') { req.reply({ body: { items: ['carrot', 'lettuce'] } }) } else { req.reply({ body: { items: [] } }) } }) uses req but req.reply is not a function. cy.intercept('GET', '/api/items', (interception) => { const type = interception.query.type if (type === 'fruit') { interception.send({ body: { items: ['apple', 'banana'] } }) } else if (type === 'vegetable') { interception.send({ body: { items: ['carrot', 'lettuce'] } }) } else { interception.send({ body: { items: [] } }) } }) uses interception.send which is not a Cypress method.

3. Final Answer:

   Option A code correctly implements dynamic response stubbing with query check and reply -> Option A

4. Quick Check:

   Use interception.reply({ body }) and check interception.query [OK]

Hint: Use interception.reply({ body }) and check interception.query.type [OK]

Common Mistakes:

• Using req.reply() which is undefined
• Omitting the body wrapper in reply
• Using interception.send() which does not exist