Stub Defined Constant

Use stub_const to stub constants. When the constant is already defined, the stubbed value will replace the original value for the duration of the example.

Stub top-level constant

Given a file named "stub_const_spec.rb" with:

FOO = 7

RSpec.describe "stubbing FOO" do
  it "can stub FOO with a different value" do
    stub_const("FOO", 5)
    expect(FOO).to eq(5)
  end

  it "restores the stubbed constant when the example completes" do
    expect(FOO).to eq(7)
  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
    FOO = 7
  end
end

module MyGem
  RSpec.describe SomeClass do
    it "stubs the nested constant when it is fully qualified" do
      stub_const("MyGem::SomeClass::FOO", 5)
      expect(SomeClass::FOO).to eq(5)
    end
  end
end

When I run rspec stub_const_spec.rb

Then the examples should all pass.

Transfer nested constants

Given a file named "stub_const_spec.rb" with:

module MyGem
  class SomeClass
    FOO = 7
  end
end

module MyGem
  RSpec.describe SomeClass do
    let(:fake_class) { Class.new }

    it "does not transfer nested constants by default" do
      stub_const("MyGem::SomeClass", fake_class)
      expect { SomeClass::FOO }.to raise_error(NameError)
    end

    it "transfers nested constants when using :transfer_nested_constants => true" do
      stub_const("MyGem::SomeClass", fake_class, :transfer_nested_constants => true)
      expect(SomeClass::FOO).to eq(7)
    end

    it "can specify a list of nested constants to transfer" do
      stub_const("MyGem::SomeClass", fake_class, :transfer_nested_constants => [:FOO])
      expect(SomeClass::FOO).to eq(7)
    end
  end
end

When I run rspec stub_const_spec.rb

Then the examples should all pass.