RSpec stub a method that's used inside a controller

I'm trying to stub a method that's called inside a controller, but it only gets stubbed within the test and not when it's called in the controller.

Target method:

class MyModel < ApplicationRecord
  def self.fetch_boolean(arg)
    MyModel.find_by({ name: arg })
    MyModel.value
  end
end

Target controller:

# controller
class OtherModelController < ApplicationController
  # ...

  if MyModel.fetch_boolean('123')
    # do something
  end

  # ...
end

RSpec test:

describe 'test' do
  before(:each) do
    allow(MyModel).to receive(:fetch_boolean).with('123').and_return(true)
  end

  it 'should do something' do
    get :show
    expect(response).to eq('hello')
  end
end

I called debugger within the RSpec test and called MyModel.fetch_boolean and got true. However, when I called it inside the controller, I got false (which is the stored value).

How do I make sure that the method inside the controller also gets stubbed?

RSpec version 3.7

Update:

Other stubbing syntaxes I've tried

allow(MyModel).to receive(:fetch_boolean).with('123') { true }
# same outcome

allow_any_instance_of(MyModel).to receive(:fetch_boolean).with('123') { true }
# error: MyModel does not implement #fetch_boolean

controller.stub(MyModel.fetch_boolean).with('123') { true }
# error: Wrong number of arguments. Expected 1, got 0

controller.stub(MyModel.fetch_boolean('123')) { true }
# error: true is not a symbol nor a string