Case Study: Wait for File Download to Complete Safely in Selenium

How to increase reliability in an automated test for a file download.

A repost of my daughter’s article, I added a few notes. This is also included in my “How to in Selenium WebDriver” series.

This article will show you how to verify a file download completes successfully in Selenium WebDriver.

Table of Contents:
∘ Test Design
∘ Fixed Wait
∘ Check the Downloaded File’s Size
∘ Wait for the Browser Download to Complete
∘ Complete Test Script
∘ Zhimin’s Notes

The test site for this article is http://zhimin.com/books/pwta. There is a sample PDF download that I will use for the tests.

Test Design

The test design is quite straightforward.

1. Click the download button
2. Wait…
3. Verify the file contents

There is an unknown factor with Step 2 — how long should we wait in the test script? And when do we know the file has finished downloading?

There are three approaches:

• Fixed wait
• Check the downloaded file’s size
• Wait for the browser download to complete ✅

Fixed Wait

This approach is very easy to understand. Just hardcode the wait time.

it "Fixed wait time" do
  driver.get("http://zhimin.com/books/pwta")
  driver.find_element(:link_text, "Download").click
  sleep 10 # wait 10 seconds
  expect(File.exist?("/Users/me/Downloads/practical-web-test-automation-sample.pdf")).to be true
end

The above file-download script is not safe, we need to
- set the custom file download path (for Chrome)
- delete the file if already exists, before clicking the ‘Download’.
This has been covered in this article, Automated Testing PDF…