Verify file download functionality

Preconditions (1)

Step 1: Click on the download button with id 'download-btn'

Step 2: Wait for the file to be downloaded

Step 3: Check the default download folder for the file named 'sample.pdf'

✅ Expected Result: The file 'sample.pdf' is downloaded successfully to the default download folder

Automation Requirements - Cypress

Assertions Needed:

Verify the file exists in the download folder

Verify the file size is greater than zero

Best Practices:

Use cy.intercept to wait for the download request

Use cy.readFile with proper path to check file existence

Avoid hardcoding absolute paths; use Cypress.config('downloadsFolder')

Clean up downloaded files before test run

Automated Solution

Cypress

/// <reference types="cypress" />

import path from 'path';

describe('File download verification', () => {
  const fileName = 'sample.pdf';
  const downloadsFolder = Cypress.config('downloadsFolder');
  const filePath = path.join(downloadsFolder, fileName);

  beforeEach(() => {
    // Clean up before test
    cy.task('deleteFile', filePath);
    cy.visit('/file-download');
  });

  it('should download the file successfully', () => {
    // Intercept the download request
    cy.intercept('GET', '/files/sample.pdf').as('fileDownload');

    // Click the download button
    cy.get('#download-btn').click();

    // Wait for the download request to complete
    cy.wait('@fileDownload');

    // Verify the file exists and is not empty
    cy.readFile(filePath, 'binary', { timeout: 15000 }).should((buffer) => {
      expect(buffer.length).to.be.greaterThan(0);
    });
  });
});

// In plugins/index.js or cypress.config.js (Node.js environment), add:
// const fs = require('fs');
// module.exports = (on, config) => {
//   on('task', {
//     deleteFile(filePath) {
//       if (fs.existsSync(filePath)) {
//         fs.unlinkSync(filePath);
//       }
//       return null;
//     }
//   });
// }

This test script uses Cypress to automate the file download verification.

We define the file name and the downloads folder path using Cypress.config('downloadsFolder') to avoid hardcoding paths.

Before each test, we delete the file if it exists to ensure a clean state.

We visit the file download page, then intercept the GET request for the file to wait for it properly.

After clicking the download button, we wait for the download request to finish.

Finally, we read the downloaded file in binary mode and assert that its size is greater than zero, confirming the file was downloaded successfully.

The deleteFile task is a Node.js helper to remove the file before the test starts, preventing false positives.

Common Mistakes - 4 Pitfalls

Not waiting for the download request to complete before checking the file

{'mistake': 'Hardcoding absolute file paths for the download folder', 'why_bad': 'This makes the test brittle and not portable across different machines or environments.', 'correct_approach': "Use Cypress.config('downloadsFolder') to get the downloads folder path dynamically."}

Not cleaning up the downloaded file before the test

{'mistake': 'Using cy.readFile without specifying encoding or mode', 'why_bad': 'Reading binary files without proper mode can cause corrupted data or wrong assertions.', 'correct_approach': "Use 'binary' encoding in cy.readFile when checking file size or content."}

Bonus Challenge

Now add data-driven testing with 3 different file names and verify each downloads correctly

Show Hint