Logo: Relish

  1. Sign in

Project: RSpec Mocks 3.2

Mutating constants


Support is provided for stubbing constants. Like with method stubs, the stubbed constants
will be restored to their original state when an example completes.

stub_const("Foo", fake_foo)
Foo # => fake_foo

Stubbed constant names must be fully qualified; the current module nesting is not

module MyGem
  class SomeClass; end

module MyGem
  describe "Something" do
    let(:fake_class) { Class.new }

    it "accidentally stubs the wrong constant" do
      # this stubs ::SomeClass (in the top-level namespace),
      # not MyGem::SomeClass like you probably mean.
      stub_const("SomeClass", fake_class)

    it "stubs the right constant" do
      stub_const("MyGem::SomeClass", fake_class)

When you stub a constant that is a module or a class, nested constants on the original
module or class are not transferred by default, but you can use the
:transfer_nested_constants option to tell rspec-mocks to transfer them:

class CardDeck
  SUITS = [:Spades, :Diamonds, :Clubs, :Hearts]
  NUM_CARDS = 52

fake_class = Class.new
stub_const("CardDeck", fake_class)
CardDeck # => fake_class
CardDeck::SUITS # => raises uninitialized constant error
CardDeck::NUM_CARDS # => raises uninitialized constant error

stub_const("CardDeck", fake_class, :transfer_nested_constants => true)
CardDeck::SUITS # => [:Spades, :Diamonds, :Clubs, :Hearts]
CardDeck::NUM_CARDS # => 52

stub_const("CardDeck", fake_class, :transfer_nested_constants => [:SUITS])
CardDeck::SUITS # => [:Spades, :Diamonds, :Clubs, :Hearts]
CardDeck::NUM_CARDS # => raises uninitialized constant error


Support is also provided for hiding constants. Hiding a constant temporarily removes it; it is
restored to its original value after the test completes.

FOO = 42
FOO => NameError: uninitialized constant FOO

Like stubbed constants, names must be fully qualified.

Hiding constants that are already undefined has no effect.



  1. Stub Defined Constant
  2. Stub Undefined Constant
  3. Hide Defined Constant
  4. Hide Undefined Constant

Last published over 7 years ago by myronmarston.