A proto-feed: Add failing tests for user model that its feed method should return all his microposts, but no others' microposts (preliminary, we will include the microposts of the users he is following later)
A proto-feed: Implement User#feed method

Techniques:
Micropost.where("user_id = ?", id)
The question mark ensures id is properly escaped before being included in the underlying SQL query, thereby avoiding SQL injection.

Note in the User model
  def feed
    Micropost.where("user_id = ?", id)
  end
is equivalent to
  def feed
    microposts
  end
A proto-feed: A test for rendering the user's feed on the Home page

Note in
expect(page).to have_selector("li##{item.id}", text: item.content)
the first # in li##{item.id} is Capybara syntax for a CSS id, whereas the second # is the beginning of a Ruby string interpolation #{}
A proto-feed: Add @feed_items instance variable in the StaticPagesController#home action
A proto-feed: Adding a status feed to the Home page, using two partials 'shared/feed_item' & 'shared/feed'

Note that 2 cases are failing now:
rspec ./spec/requests/micropost_pages_spec.rb:14 # MicropostPages micropost creation with invalid information should not create a micropost
rspec ./spec/requests/micropost_pages_spec.rb:20 # MicropostPages micropost creation with invalid information error messages
This is because in 'shared/feed' we have '<% if @feed_items.any? %>' on the first line
However if signed-in user posts invalid micropost, we call:
  render 'static_pages/home'
In MicropostsController#create. Thus if code goes to this branch, the instance variable @feed_items is nil.
(Remember in Rails MVC framework, HTTP request is first handled by controller action according to router, then forward to a view for rendering. All instance variables in the controller action will be auto visible in the view)
A proto-feed: Get the tests green by assign @feed_items to an empty array in MicropostsController#create action

This is a quick fix, however if you click 'Post' with invalid content, you will see empty feed list on home page