Selenium Python Login Form Validation Testing | 35 Test Cases Automated

The login form is one of the most critical features in any web application. When validation doesn’t work correctly, users can’t log in — and worse, it can open the door to serious security issues like SQL injection and unauthorized access. That’s why automating comprehensive testing before release is so important.

Testing a login form manually is surprisingly tedious. Full-width characters, empty strings, SQL injection, emojis — the list of things to check just keeps growing. In this article, we’ll walk through a Python script that automatically runs 35 login form validation test cases using Selenium. Results are exported as CSV and JSON, and screenshots are saved automatically on any FAIL.

Test Perspectives

This script covers the following test perspectives comprehensively. These are standard perspectives used in real QA workflows, so you can apply them directly to your own product’s test design.

Test Cases (All 35)

The test cases are organized into 4 categories, with extra coverage for full-width characters and special characters — areas that are often overlooked in real-world QA.

Setup & How to Run

Install Required Libraries

Just install these two libraries and you’re ready. No manual ChromeDriver management needed.

pip install selenium webdriver-manager

Run Commands

# Run with browser visible (default)
python form_validation_test.py

# Headless mode (no browser window — great for CI)
python form_validation_test.py --headless

Sample Output

Results stream to the terminal in real time. For FAIL cases, the reason and screenshot path are displayed together.

==============================================================
  Selenium Form Validation Test (headless)
  Target : //the-internet.herokuapp.com/login
  Cases  : 35
  Start  : 2025-07-01 10:00:00
==============================================================
  (01/35) Full-width alpha username      ... ✅ PASS (1823ms)
  (02/35) Full-width numeric password    ... ✅ PASS (1654ms)
  (03/35) Full-width space in username   ... ✅ PASS (1701ms)
  ...
  (09/35) Valid login (correct creds)    ... ❌ FAIL (2100ms)
       → expected_error:True / actual_error:False
       📸 screenshots/H-01_FAIL.png
  ...
  (35/35) URL-encoded characters         ... ✅ PASS (1590ms)

──────────────────────────────────────────────────────────────
  Test Summary
──────────────────────────────────────────────────────────────
  Total  : 35
  ✅ PASS  : 34
  ❌ FAIL  : 1
  ⚠️  ERROR : 0
  Rate   : 97.1%
──────────────────────────────────────────────────────────────

Code Walkthrough: 3 Key Points

① Injecting Values via JavaScript

Selenium’s send_keys() can fail to correctly input special characters like newlines (\n) or tabs (\t). By setting values directly via JavaScript, you can safely input any character.

arguments[0] takes the WebElement and arguments[1] takes the string to input. This bypasses browser key event processing and writes directly to the DOM element. Characters that tend to break with send_keys() — emoji, full-width characters, control characters — all work reliably this way. Test cases S-05 (newline) and S-06 (tab) only work because of this approach.

driver.execute_script("arguments[0].value = arguments[1];", u_elem, tc["username"])
driver.execute_script("arguments[0].value = arguments[1];", p_elem, tc["password"])

② Bypassing HTML5 Validation

Empty string tests (L-01 ~ L-03) would normally be blocked by the browser due to the HTML5 required attribute. Adding novalidate lets the request reach the server so you can verify server-side behavior.

The real goal of validation testing isn’t “did the browser show an error?” — it’s “does the server correctly return an error?” By intentionally disabling front-end validation, you can directly test the robustness of your back end.

driver.execute_script(
    "document.querySelector('form').setAttribute('novalidate','true');"
)

③ Saving Screenshots Only on FAIL

Taking screenshots for every test case creates an overwhelming number of files. Saving only on FAIL keeps things clean and makes it much easier to investigate issues later.

Files are named {testID}_FAIL.png, so you can tell exactly which test case failed just from the filename. When running in CI/CD environments like GitHub Actions, saving these screenshots as artifacts dramatically speeds up debugging.

if r.status == "FAIL":
    os.makedirs("screenshots", exist_ok=True)
    ss = f"screenshots/{tc['id']}_FAIL.png"
    driver.save_screenshot(ss)
    r.screenshot = ss

Auto-Export Reports as CSV & JSON

After the tests finish, timestamped report files are generated automatically.

📄 report_20250701_100000.csv
📄 report_20250701_100000.json

Ideas to Take It Further

Pitfalls & Lessons Learned

Here are the key issues I encountered during implementation. I hope this helps others who run into the same problems.

① Special Characters Are Not Entered Correctly with send_keys()

When entering special characters such as newlines (\n), tabs (\t), or emojis using send_keys(), the text sometimes got garbled or caused unexpected behavior. The solution was to write values directly to the DOM via JavaScript.

# ❌ send_keys() may garble special characters
username_field.send_keys("test\nuser")

# ✅ Use JS to set the value directly
driver.execute_script("arguments[0].value = arguments[1];", username_field, "test\nuser")

💡 Key Takeaway： Pass the WebElement as arguments[0] and the input string as arguments[1]. This bypasses the browser’s key event processing and reliably writes the value directly.

② Browser Blocks Submission Due to HTML5 required Attribute

When attempting to run empty string tests, the form’s required attribute caused the browser to block the request before it reached the server, making it impossible to verify server-side behavior.

# ❌ required attribute blocks the request at the browser level
submit_button.click()

# ✅ Add novalidate to bypass HTML5 validation
driver.execute_script(
    "document.querySelector('form').setAttribute('novalidate', 'true');"
)
submit_button.click()

💡 Key Takeaway： The true purpose of validation testing is not just “the browser shows no error” but “does the server correctly return an error?” Always test server-side behavior directly.

③ Taking Screenshots for All Cases Created Too Many Files

Initially I captured screenshots for all 35 cases, which generated a huge number of files and made it hard to identify what was important. Switching to a design that only saves screenshots on FAIL made management much easier.

# ❌ Saving all cases creates too many files
driver.save_screenshot(f"screenshots/{tc['id']}.png")

# ✅ Only save on FAIL
if result.status == "FAIL":
    os.makedirs("screenshots", exist_ok=True)
    driver.save_screenshot(f"screenshots/{tc['id']}_FAIL.png")

💡 Key Takeaway： Using the format {testID}_FAIL.png lets you identify which test case failed just by looking at the filename.

④ A Wrong Expected Value Caused Continuous FAIL Results

I had mistakenly set expected_error: True on the valid login test case (H-01), which meant the test kept showing FAIL even though login was succeeding correctly. Mistakes in expected values are easy to overlook during debugging.

# ❌ Wrong expected value causes FAIL even on correct behavior
{"id": "H-01", "username": "tomsmith", "password": "SuperSecretPassword!", "expected_error": True}

# ✅ Correct: expected_error should be False for a valid login
{"id": "H-01", "username": "tomsmith", "password": "SuperSecretPassword!", "expected_error": False}

⚠️ Note： When a test fails, always first determine whether it is a “code bug” or an “expected value mistake” before diving into debugging.

⑤ Retrieving Error Messages Too Soon After Submission

Immediately after submitting the form, the page had not yet updated, so trying to retrieve the error message resulted in the element not being found. A wait after submission was necessary.

# ❌ Grabbing the error right after submit may fail
submit_button.click()
error = driver.find_element(By.ID, "flash")

# ✅ Use WebDriverWait to wait until the element appears
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC

submit_button.click()
error = WebDriverWait(driver, 10).until(
    EC.presence_of_element_located((By.ID, "flash"))
)

💡 Key Takeaway： Conditional waits with WebDriverWait are faster and more stable than fixed waits with time.sleep().

Summary

In this article, we walked through how to automate login form validation testing with Selenium and Python.

In real-world practice, these tests are integrated into a CI/CD pipeline and run automatically on every pull request, enabling continuous quality verification. Selenium tests are widely used for regression testing — ensuring the login flow works correctly on every deployment.

The full source code is available on GitHub. Give it a try in your own environment! By swapping out the target form, you can apply this to virtually any web application. Feel free to leave questions in the comments below 👇