外部gemなしに定数のstub化したい場合

stub_constant.rb

class Foo
  BAR = 'bar'
end

class FooTest < ActiveSupport::TestCase
  setup do
    @original = Foo.send(:remove_const, :BAR)
    Foo.const_set(:BAR, 'new_value')
  end
  
  teardown do
    Foo.send(:remove_const, :BAR)
    Foo.const_set(:BAR, @original)
  end
  
  test 'Foo::BARのテスト' do
    assert_equal 'new_value', Foo::BAR
  end
end