Creating Fixtures from Response Bodies dynamically using Cypress Exec(), a practical approach

cy.exec() is used to execute shell commands directly within your Cypress tests. This feature enables you to interact with the underlying operating system, perform tasks such as working with the file system, running build scripts, seeding your test database, starting processes, killing processes or executing any other command-line operations needed during your tests.

In this article, we explore how the cy.exec() command can be utilized to handle test fixtures effectively by creating fixtures from response bodies dynamically, along with examples and best practices.

Understanding Test Fixtures: Test fixtures are pre-defined data used as inputs for executing tests. These fixtures would include JSON files, database snapshots, or any other data source required for test scenarios.

Use Case: Creating Fixtures from API Responses

In this scenario ,we are using exec() to write to a file to create a fixture from response body

cy.intercept('POST', '/comments').as('postComment')
cy.get('.add-comment').click()
cy.wait('@postComment').then(({ response }) => {
//execute shell command 
 cy.exec(
    `echo ${JSON.stringify(response.body)} >cypress/fixtures/comment.json`
  )
  cy.fixture('comment.json').should('deep.eq', response.body)
})

//Reads data from comment.json fixture
cy.fixture('comment.json').then((commentData) => {
      // Use the commentData in your test
      console.log(commentData);
      // Add assertions or other test logic here
    });

Lets breakdown the command cy.exec()

• The backticks `` are used for template literals in JavaScript, allowing embedded expressions.
• The echo command is used to output text.
• ${JSON.stringify(response.body)} is an embedded expression that converts the response.body object into a JSON string.
• > is a shell commands, used to redirect the output of the preceding command to a file.
• cypress/fixtures/comment.json specifies the path and filename where the output of the echo command will be written.

This approach helps to verify the intercepted data from the API against the UI, or for other assertions .

Usage Considerations:

• Ensure that the response.body object contains valid JSON data. Otherwise, the JSON.stringify() function may throw an error.
• Keep in mind that using cy.exec() to write fixture files can be useful for capturing dynamic or changing data during test runs, but it may introduce dependencies on the local environment or require additional clean up steps in test suites.

I would like to acknowledge the Cypress documentation for its comprehensive resources and helpful examples that enriched the content of this article.