(Rspec) expected #count to have changed by 1, but was changed by 0 - ruby-on-rails-5

Question

I started to learn Rspec one day ago. When writing test for my articles controller, I got error at create new article. Here is my controller:
def create
Article.transaction do
begin
#article = Article.new(article_params)
respond_to do |format|
if #article.save
view_context.create_sitemap
flash[:show_alert] = true
format.html { redirect_to edit_admin_article_path(#article), notice: 'Created sucessfull' }
else
format.html { render :new }
format.json { render json: #article.errors,notice: "Unprocessable entity" }#may need a helper to handle exception
end
end
rescue Exception => e
raise ActiveRecord::Rollback
respond_to do |format|
flash[:show_alert] = true
format.html { redirect_to new_admin_article_path, notice: 'Create failed'}
end
end
end
end
here is my test:
describe "POST #create" do
context "with valid attributes" do
it "creates a new article" do
expect{
post :create, params: { article: FactoryGirl.attributes_for(:article) }
}.to change(Article, :count).by(1)
end
it "redirects to the index page" do
post :create, params: { article: FactoryGirl.attributes_for(:article) }
expect(response).to redirect_to admin_articles_path
end
end
context "with invalid attributes" do
it "does not save the new article" do
expect{
post :create, params: { article: FactoryGirl.attributes_for(:article) }
}.to_not change(Article, :count).by(1)
end
it "re-renders the :new template" do
post :create, params: { article: FactoryGirl.attributes_for(:article) }
expect(response).to render_template :new
end
end
end
And here is the log:
3) Admin::ArticlesController POST #create with valid attributes creates a new article
Failure/Error:
expect{
post :create, params: { article: FactoryGirl.attributes_for(:article) }
}.to change(Article, :count).by(1)
expected #count to have changed by 1, but was changed by 0
# ./spec/controllers/admin/articles_controller_spec.rb:29:in `block (4 levels) in <top (required)>'
I spent time to search for the same issue but, all of them didn't solve my error. My problem is I cannot find out where the error come from. Any help is appreciated.