Cucumber is a powerful tool for behavior-driven development (BDD), helping bridge the gap between business and technical teams by writing tests in human-readable language. A key feature in Cucumber is its ability to handle regular expressions (regex), which allows flexible matching of text patterns in steps, making the tests more dynamic and reusable.
In this post, we’ll explore how to use regular expressions in Cucumber step definitions, along with some practical examples and tips.
What are Regular Expressions?
Regular expressions are sequences of characters that define search patterns. In Cucumber, regular expressions are used to match step definitions with feature file scenarios, allowing flexibility when dealing with dynamic values like numbers, dates, or varying text formats.
Why Use Regular Expressions in Cucumber?
- Dynamic Value Matching: You can match different input values (e.g., usernames, dates, or amounts) without writing separate steps for each case.
- Code Reusability: Instead of creating multiple step definitions for different scenarios, regular expressions allow you to define one reusable step.
- Simplified Test Scenarios: You can keep your feature files concise by allowing dynamic placeholders.
Basic Syntax of Regular Expressions in Cucumber
In Cucumber, regular expressions are placed inside the step definition annotations like Given, When, or Then. Here’s a simple example:
@When("^I enter the amount (\\d+)$")
public void i_enter_the_amount(int amount) {
// code to handle the entered amount
}
- The ^ and $ are used to denote the start and end of the pattern.
- (\\d+) is a regular expression pattern that matches one or more digits. The value captured by this pattern is passed to the step definition as the argument amount.
Common Regular Expression Patterns in Cucumber
Here are a few common regex patterns you might encounter:
1. Numbers: (\\d+) matches a sequence of digits (i.e., numbers). Example:
@When("^I have (\\d+) apples$")
public void i_have_apples(int apples) {
// apples can be any number
}
2. Text: (.+) matches any text (except line breaks). Example:
@Given("^the user name is (.+)$")
public void the_user_name_is(String username) {
// username can be any string
}
3. Specific Word: You can also match a specific word with a regex. Example:
@Then("^the message should be \"([a-zA-Z ]+)\"$")
public void the_message_should_be(String message) {
// message should only contain letters and spaces
}
4. Dates: You can match date formats using regular expressions. Example:
@When("^the date is (\\d{2}/\\d{2}/\\d{4})$")
public void the_date_is(String date) {
// Matches dates in format DD/MM/YYYY
}
Examples of Regular Expressions in Cucumber
1. Matching Dynamic Numbers
Suppose you want to test an ATM scenario where a user withdraws various amounts:
Feature File:
Scenario: Withdraw money
When I withdraw 100 dollars
Then my account balance should be 900 dollars
Step Definition:
@When("^I withdraw (\\d+) dollars$")
public void i_withdraw_dollars(int amount) {
// Logic to withdraw money
}
The regular expression (\\d+) allows you to match different amounts without needing a new step definition for each scenario.
2. Capturing Multiple Dynamic Values
You can capture multiple dynamic values in a single step using multiple regex patterns:
Feature File:
Scenario: Transfer funds
When I transfer 500 dollars from account A to account B
Step Definition:
@When("^I transfer (\\d+) dollars from account (.+) to account (.+)$")
public void i_transfer_funds(int amount, String fromAccount, String toAccount) {
// Logic to transfer funds between accounts
}
In this case, (\\d+) captures the transfer amount, and (.+) captures the account names.
Tips for Writing Effective Regular Expressions in Cucumber
- Keep It Simple: Use regex only when necessary. If you don’t need to match a variable, avoid regex to keep your step definitions easy to read.
- Test Your Regex: Always test your regular expressions using tools like regex101 to ensure they work as expected before using them in step definitions.
- Avoid Overcomplication: Don’t try to capture too many variables in one step. If a step becomes overly complex, break it into smaller steps for better readability.
- Use Named Groups (Cucumber Expressions): Cucumber also supports “Cucumber Expressions” as an alternative to regular expressions. These provide a simpler syntax for defining steps:
@When("I withdraw {int} dollars")
public void i_withdraw_dollars(int amount) {
// Simpler alternative to regular expressions
}
Conclusion
Regular expressions in Cucumber add flexibility to your test scenarios, enabling you to write more reusable and dynamic step definitions. However, like any powerful tool, they should be used judiciously to maintain readability and simplicity in your test automation codebase.
By mastering regex patterns, you can ensure your tests are concise, efficient, and capable of handling various dynamic inputs, making your BDD practices more effective.