snippets.md

Snippets

Often in a BDD workflow, you'll write one or more steps in a feature file before implementing the corresponding step definition(s). When you run cucumber-js and it finds these undefined steps, it will generate a Snippet for each one - a skeletal chunk of JavaScript with the correct expression and arguments that you can drop into your code to get started. Formatters that are designed for the terminal will output the snippets.

Let's say we're iterating on this feature:

Feature: Removing todos

  Scenario: Add and then remove a todo from an empty list
    Given an empty todo list
    When I add the todo "buy some cheese"
    And I remove the todo "buy some cheese"

The last step about removing todos isn't implemented yet - we just wrote that into the scenario, so now it's time to write the step definition. If we run cucumber-js, it will announce the undefined step and provide the Snippet in the output:

Then('I remove the todo {string}', function (string) {
  // Write code here that turns the phrase above into concrete actions
  return 'pending';
});

By default, the snippet uses the "synchronous" style. You can use the snippetInterface format option to specify one of the styles that supports asynchronous steps:

• "async-await" - Outputs an async function where you can use await - probably the best choice if you aren't sure. Running with --format-options '{"snippetInterface":"async-await"}' yields:

  Then('I remove the todo {string}', async function (string) {
    // Write code here that turns the phrase above into concrete actions
    return 'pending';
  });

• "callback" - Outputs a plain function with a callback function as the final argument. Running with --format-options '{"snippetInterface":"callback"}' yields:

  Then('I remove the todo {string}', function (string, callback) {
    // Write code here that turns the phrase above into concrete actions
    callback(null, 'pending');
  });

• "promise" - Outputs a plain function from which you should return a Promise. Running with --format-options '{"snippetInterface":"promise"}' yields:

  Then('I remove the todo {string}', function (string) {
    // Write code here that turns the phrase above into concrete actions
    return Promise.resolve('pending');
  });

• "synchronous" - Outputs a plain function with no async pattern (see earlier example).

Options

These format options influence how the snippets are rendered by all formatters that output snippets:

• snippetInterface - set to one of 'async-await', 'callback', 'promise', or 'synchronous' to alter the style of generated snippets for undefined steps
• snippetSyntax - module name of path of the custom snippet syntax to be used