Use rspec-core without rspec-mocks or rspec-expectations

It is most common to use rspec-core with rspec-mocks and rspec-expectations, and rspec-core will take care of loading those libraries automatically if available, but rspec-core can be used just fine without either of those gems installed.

Use only rspec-core when only it is installed

Given only rspec-core is installed

And a file named “coreonlyspec.rb” with:

RSpec.describe "Only rspec-core is available" do
  it "it fails when an rspec-mocks API is used" do
    dbl = double("MyDouble")

  it "it fails when an rspec-expectations API is used" do
    expect(1).to eq(1)

When I run rspec core_only_spec.rb

Then the output should contain “2 examples, 2 failures”.