Using Regular Expressions for API Automation Testing: 10 Practical Examples

Regular expressions (regex) are extremely useful in API automation testing for extracting specific information from responses and validating that returned content matches expected formats.

Example 1: Extract URLs from HTML

import re
html = 'Example Visit Test Site'
pattern = re.compile(r'href="(http[s]?://(?:[a-zA-Z0-9$-_@.&+]|[!*\\(\\),]|(?:%[0-9a-fA-F][0-9a-fA-F]))+)'")
matches = pattern.findall(html)
print(matches)  # ['https://www.example.com', 'http://test.example.org']

Example 2: Validate Email Format

email = "[email protected]"
pattern = re.compile(r'^[\w\.-]+@[\w\.-]+\.\w+$')
if pattern.match(email):
    print("Valid email")
else:
    print("Invalid email")  # Valid email

Example 3: Extract Specific Field from JSON Response

json_text = '{"name": "John Doe", "age": 30, "city": "New York"}'
pattern = re.compile(r'"age": (\d+)')
match = pattern.search(json_text)
if match:
    age = match.group(1)
    print(f"Age: {age}")  # Age: 30
else:
    print("Age not found")

Example 4: Match Phone Numbers

text = "Contact us at +1 (123) 456-7890 or +44-20-7123-4567."
pattern = re.compile(r'\+?\d{1,3}[-.\s]?\(?\d{3}\)?[-.\s]?\d{3}[-.\s]?\d{4}')
phone_numbers = pattern.findall(text)
print(phone_numbers)  # ['+1 (123) 456-7890', '+44-20-7123-4567']

Example 5: Detect Sensitive Words in a Message

message = "Your order has been processed successfully."
sensitive_words = ["error", "failed"]
pattern = re.compile("|".join(map(re.escape, sensitive_words)))
if pattern.search(message):
    print("Message contains sensitive words.")
else:
    print("Message is clean.")  # Message is clean.

Example 6: Extract HTTP Status Code from Log

log_entry = "GET /api/data HTTP/1.1 200 OK"
pattern = re.compile(r'\b\d{3}\b')
status_code = pattern.search(log_entry)
if status_code:
    print(f"Status Code: {status_code.group()}")  # Status Code: 200
else:
    print("No status code found.")

Example 7: Validate Date Format (YYYY-MM-DD)

date_str = "2023-04-01"
pattern = re.compile(r'^\d{4}-\d{2}-\d{2}$')
if pattern.match(date_str):
    print("Valid date format")
else:
    print("Invalid date format")  # Valid date format

Example 8: Extract Query Parameter from URL

url = "https://www.example.com/search?q=python+regex⟨=en"
pattern = re.compile(r'q=(.*?)(&|$)')
match = pattern.search(url)
if match:
    query = match.group(1)
    print(f"Search Query: {query}")  # Search Query: python+regex
else:
    print("Query parameter not found")

Example 9: Check Password Strength

password = "P@ssw0rd"
pattern = re.compile(r'^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$')
if pattern.match(password):
    print("Strong password")
else:
    print("Weak password")  # Strong password

Example 10: Extract Content from XML Tag

xml_data = 'Some description here.'
pattern = re.compile(r'')
title = pattern.search(xml_data).group(1)
print(title)  # Sample Title

These ten examples illustrate how regex can be leveraged to efficiently parse and validate various data formats encountered during API testing.