A Step Definition is a with an expression that links it to one or more Gherkin steps. When Cucumber executes a Gherkin step in a scenario, it will look for a matching step definition to execute.

To illustrate how this works, look at the following Gherkin Scenario:

Scenario: Some cukes
  Given I have 48 cukes in my belly

The I have 48 cukes in my belly part of the step (the text following the Given keyword) will match the following step definition:

Expressions

A step definition’s expression can either be a Regular Expression or a Cucumber Expression. The examples in this section use Cucumber Expressions. If you prefer to use Regular Expressions, each capture group from the match will be passed as arguments to the step definition’s .

If the capture group expression is identical to one of the registered parameter types’s regexp, the captured string will be transformed before it is passed to the step definition’s . In the example above, the cukes argument will be an integer, because the built-in int parameter type’s regexp is \d+ .

State management

A step definition can transfer state to a subsequent step definition by storing state in instance variables.

Scope

Step definitions aren’t linked to a particular feature file or scenario. The file, class or package name of a step definition does not affect what Gherkin steps it will match. The only thing that matters is the step definition’s expression.

Snippets

When Cucumber encounters a Gherkin step without a matching step definition, it will print a step definition snippet with a matching Cucumber Expression. You can use this as a starting point for new step definitions.

Consider this Gherkin step:

Given I have 3 red balls

If you don’t have a matching step definition, Cucumber will suggest the following snippet:

Suggested snippets will use your own parameter types if they match parts of your undefined step. If a color parameter type exists, Cucumber would use that in the suggested expression:

Make sure you use the summary plugin when running Cucumber in order to have the snippets printed.

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