Syntax Configuration

The primary syntax provided by rspec-expectations is based on the expect method, which explicitly wraps an object or block of code in order to set an expectation on it.

There’s also an older should-based syntax, which relies upon should being monkey-patched onto every object in the system. However, this syntax can at times lead to some surprising failures, since RSpec does not own every object in the system and cannot guarantee that it will always work consistently.

We recommend you use the expect syntax unless you have a specific reason you prefer the should syntax. We have no plans to ever completely remove the should syntax but starting in RSpec 3, a deprecation warning will be issued if you do not explicitly enable it, with the plan to disable it by default in RSpec 4 (and potentially move it into an external gem).

If you have an old should-based project that you would like to upgrade to the expect, check out transpec, which can perform the conversion automatically for you.

Background

Given a file named “spec/syntaxes_spec.rb” with:

require 'spec_helper'

RSpec.describe "using the should syntax" do
  specify { 3.should eq(3) }
  specify { 3.should_not eq(4) }
  specify { lambda { raise "boom" }.should raise_error("boom") }
  specify { lambda { }.should_not raise_error }
end

RSpec.describe "using the expect syntax" do
  specify { expect(3).to eq(3) }
  specify { expect(3).not_to eq(4) }
  specify { expect { raise "boom" }.to raise_error("boom") }
  specify { expect { }.not_to raise_error }
end

Both syntaxes are available by default

Given a file named “spec/spec_helper.rb” with:

When I run rspec

Then the examples should all pass

And the output should contain “Using should from rspec-expectations’ old :should syntax without explicitly enabling the syntax is deprecated”.

Disable should syntax

Given a file named “spec/spec_helper.rb” with:

RSpec.configure do |config|
  config.expect_with :rspec do |expectations|
    expectations.syntax = :expect
  end
end

When I run rspec

Then the output should contain all of these:

Disable expect syntax

Given a file named “spec/spec_helper.rb” with:

RSpec.configure do |config|
  config.expect_with :rspec do |expectations|
    expectations.syntax = :should
  end
  config.mock_with :rspec do |mocks|
    mocks.syntax = :should
  end
end

When I run rspec

Then the output should contain all of these:

Explicitly enable both syntaxes

Given a file named “spec/spec_helper.rb” with:

RSpec.configure do |config|
  config.expect_with :rspec do |expectations|
    expectations.syntax = [:should, :expect]
  end
end

When I run rspec

Then the examples should all pass

And the output should not contain “deprecated”.