rspec testing if method is called in controller spec

How can I test if a method is called in controller? The second test passes but the first one fails and thorws this error:

Failure/Error: expect(@user).to receive(:decreasing_comment_notification_number).with("Post", post.id)

   (#<User:0x007fd6f6312db8>).decreasing_comment_notification_number("Post", 1)
       expected: 1 time with arguments: ("Post", 1)
       received: 0 times

controller

def dropdown_checking_decreasing
  current_user.decreasing_comment_notification_number(params[:notifiable_type], params[:notifiable_id])
  redirect_to notification_redirection_path(params[:notifiable_type], params[:notifiable_id])
end

test

context "GET dropdown_checking_decreasing" do
  let!(:post) { create(:post, user: @user,) }
  let!(:notification) { create(:notification, sender: user, recipient: @user, notifiable_type: "Post", notifiable_id: post.id) }

  it "invokes decreasing_comment_notification_number on current user" do
    expect(@user).to receive(:decreasing_comment_notification_number).with("Post", post.id)
    get :dropdown_checking_decreasing, user_id: @user.id, notifiable_type: notification.notifiable_type, notifiable_id: notification.notifiable_id
  end

  it "redirects to notifiable" do
    get :dropdown_checking_decreasing, user_id: @user.id, notifiable_type: notification.notifiable_type, notifiable_id: notification.notifiable_id
    expect(response).to redirect_to "/posts#post_#{notification.notifiable_id}"
  end
end