RSpec Expectations

Introduction#

RSpec::Expectations lets you express expected outcomes on an object using an example-based DSL syntax.

Remarks#

This topic gives examples of how to expect test results in RSpec using expect .to and the many built-in matchers.

This functionality is provided by the rspec-expectations gem.

Basic Usage

Given a class as follows:

class Cube
  attr_reader :height, :width, :depth

  def initialize(args)
    @height = args[:height] || args[:y] || 1
    @width  = args[:width]  || args[:x] || 1
    @depth  = args[:depth]  || args[:z] || 1
  end

  def volume
    height * width * depth
  end
end

The following example passes if cube.volume equals 60 and fails if it doesn’t. It uses the most commonly used built-in matcher, eq, which just tests for equality.

RSpec.describe Cube do
  it "calculates it's volume" do
    cube = Cube.new(x: 3, y: 4, z: 5)
    expect(cube.volume).to eq(60)
  end
end