Stub ENV doesn't work for Rspec cottroller test

I come into the task for implementing https redirect for my app. After discuss with team, we should to go with simple redirect way.

And this is the the code in controller:

application_controller.rb (version 1)

class ApplicationController < ActionController::Base
  ...

    def self.force_ssl(options = {})
      return unless ENV["FORCE_SSL"].present?
      host = options.delete(:host)
      before_filter(options) do
        if !request.ssl? && params[:controller] != "health_check"
          redirect_to request.url.gsub("http://", "https://")
        end
      end
    end

    force_ssl

  ...
end

The problem is when I stub the ENV['FORCE_SSL'] in controller test. It not work. ENV is correctly stub when run pry.binding in test suite but when I run pry.binding in force_ssl method when test is running, ENV['FORCE_SSL'] is nil.

Code in spec file:

require 'rails_helper'

RSpec.describe ApplicationController, type: :controller do

  controller do
    def index
      redirect_to root_path
    end
  end

  it "redirect to https when request in http" do
    allow(ENV).to receive(:[]).with('FORCE_SSL').and_return('true')

    get 'index', protocal: :http
    expect(response).to redirect_to %r(\Ahttps://)
  end
end

After that, when I change force_ssl to instance method gracefully.

application_controller.rb (version 2)

class ApplicationController < ActionController::Base
 ...

  before_action :force_ssl

  private

    def force_ssl
      return unless ENV["FORCE_SSL"].present?

      if !request.ssl? && params[:controller] != "health_check"
        redirect_to request.url.gsub("http://", "https://")
      end
    end
...
end

Just want to know the reason why this happen and are there any way to stub the ENV for test with version 1 controller code ?