Stub Undefined Constant

Use stub_const to stub constants. When the constant is not already defined, all the necessary intermediary modules will be dynamically created. When the example completes, the intermediary module constants will be removed to return the constant state to how it started.

Stub top-level constant

Given a file named "stub_const_spec.rb" with:

RSpec.describe "stubbing FOO" do
  it "can stub undefined constant FOO" do
    stub_const("FOO", 5)
    expect(FOO).to eq(5)
  end

  it "undefines the constant when the example completes" do
    expect { FOO }.to raise_error(NameError)
  end
end

When I run rspec stub_const_spec.rb

Then the examples should all pass.

Stub nested constant

Given a file named "stub_const_spec.rb" with:

module MyGem
  class SomeClass
  end
end

module MyGem
  RSpec.describe SomeClass do
    it "can stub an arbitrarily deep constant that is undefined" do
      expect(defined?(SomeClass::A)).to be_falsey
      stub_const("MyGem::SomeClass::A::B::C", 3)
      expect(SomeClass::A::B::C).to eq(3)
      expect(SomeClass::A).to be_a(Module)
    end

    it 'undefines the intermediary constants that were dynamically created' do
      expect(defined?(SomeClass)).to be_truthy
      expect(defined?(SomeClass::A)).to be_falsey
    end
  end
end

When I run rspec stub_const_spec.rb

Then the examples should all pass.