rspec-expectations is used to define expected outcomes.

describe Account do
  it "has a balance of zero when first created" do
    expect(Account.new.balance).to eq(Money.new(0))
  end
end

Basic structure

The basic structure of an rspec expectation is:

expect(actual).to matcher(expected)
expect(actual).not_to matcher(expected)

Note: You can also use expect(..).to_not instead of expect(..).not_to. One is an alias to the other, so you can use whichever reads better to you.

Examples

expect(5).to eq(5)
expect(5).not_to eq(4)

What is a matcher?

A Matcher is any object that responds to the following methods:

matches?(actual)
failure_message_for_should

These methods are also part of the matcher protocol, but are optional:

does_not_match?(actual)
failure_message_for_should_not
description

RSpec ships with a number of built-in matchers and a DSL for writing custom matchers.

Issues

The documentation for rspec-expectations is a work in progress. We'll be adding Cucumber features over time, and clarifying existing ones. If you have specific features you'd like to see added, find the existing documentation incomplete or confusing, or, better yet, wish to write a missing Cucumber feature yourself, please submit an issue or a pull request.