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Cucumber Expressions

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Cucumber Expressions are a way to define patterns for step definitions in Cucumber, allowing for more readable and maintainable test scripts. They provide an alternative to regular expressions, making it easier to write and understand step definitions.

Key Concepts of Cucumber Expressions

  1. Simplified Syntax: Cucumber Expressions use a simpler syntax compared to regular expressions, making them more accessible to non-technical stakeholders.
  2. Parameter Types: They allow the use of parameter types to automatically convert strings in steps to specific data types.
  3. Custom Parameter Types: You can define custom parameter types to handle specific data conversions.
  4. Optional Text: Cucumber Expressions support optional text, which can be included or excluded in the step.

Comparison: Cucumber Expressions vs. Regular Expressions

Feature Cucumber Expressions Regular Expressions
Syntax Complexity Simple and readable Complex and less readable
Parameter Handling Built-in parameter types Manual conversion required
Customization Supports custom parameter types Requires custom regex patterns
Optional Text Supported with brackets {} Requires complex regex patterns

Practical Example

Let's explore how to use Cucumber Expressions with a practical example.

Step Definition with Regular Expression

@Given("^I have (\\d+) cucumbers in my basket$")
public void i_have_cucumbers_in_my_basket(int cucumbers) {
    System.out.println("Cucumbers in basket: " + cucumbers);
}

Step Definition with Cucumber Expression

@Given("I have {int} cucumbers in my basket")
public void i_have_cucumbers_in_my_basket(int cucumbers) {
    System.out.println("Cucumbers in basket: " + cucumbers);
}

Explanation

  • Regular Expression: Uses \\d+ to capture digits and requires manual conversion to an integer.
  • Cucumber Expression: Uses {int} to automatically convert the captured value to an integer.

Using Parameter Types

Cucumber Expressions support several built-in parameter types:

  • {int}: Matches integers.
  • {float}: Matches floating-point numbers.
  • {word}: Matches a single word.
  • {string}: Matches a quoted string.

Example with Multiple Parameter Types

@When("I add {int} {word} to the basket")
public void i_add_items_to_the_basket(int quantity, String item) {
    System.out.println("Added " + quantity + " " + item + " to the basket");
}

Custom Parameter Types

You can define custom parameter types to handle specific data conversions.

Defining a Custom Parameter Type

ParameterTypeRegistry registry = new ParameterTypeRegistry(Locale.ENGLISH);
registry.defineParameterType(new ParameterType<>(
    "color",                   // Name
    "red|blue|green",         // Regex
    Color.class,              // Type
    Color::new                // Transformer
));

Using a Custom Parameter Type

@Then("the color should be {color}")
public void the_color_should_be(Color color) {
    System.out.println("Color is: " + color);
}

Optional Text

Cucumber Expressions allow optional text using parentheses ().

Example with Optional Text

@Then("I should see {int} (more )?cucumbers")
public void i_should_see_cucumbers(int count) {
    System.out.println("Cucumbers seen: " + count);
}

Practical Exercise

Exercise: Write a Cucumber Expression for the following scenario:

  • Scenario: Add items to the cart
    • Given I have 3 apples in my cart
    • When I add 2 bananas to the cart
    • Then I should see 5 items in the cart

Solution:

@Given("I have {int} apples in my cart")
public void i_have_apples_in_my_cart(int apples) {
    System.out.println("Apples in cart: " + apples);
}

@When("I add {int} bananas to the cart")
public void i_add_bananas_to_the_cart(int bananas) {
    System.out.println("Bananas added: " + bananas);
}

@Then("I should see {int} items in the cart")
public void i_should_see_items_in_the_cart(int totalItems) {
    System.out.println("Total items in cart: " + totalItems);
}

Common Mistakes and Tips

  • Mistake: Forgetting to match the parameter type in the step definition.
    • Tip: Ensure the parameter type in the Cucumber Expression matches the method parameter type.
  • Mistake: Using complex regular expressions unnecessarily.
    • Tip: Use Cucumber Expressions for simplicity and readability.

Conclusion

Cucumber Expressions provide a powerful and user-friendly way to define step definitions in Cucumber. By using built-in and custom parameter types, you can create more readable and maintainable test scripts. Practice using Cucumber Expressions to become proficient in writing clear and concise BDD scenarios.

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