Capybara unable to find field "search" - ruby-on-rails

Question

I tried setting the id in various parts of the form, as well as wrapping the form in a div with id set to search. The result is always the same.
spec/features/02_post_spec.rb
scenario 'search for post title' do
fill_post_form(post3)
fill_in "search", with: post3.title
click_button("Search")
expect(page).to_not have_content(post1.title)
expect(page).to_not have_content(post2.title)
expect(page).to have_content(post3.title)
end
spec/spec_helper.rb
def fill_post_form(post)
visit new_post_path
fill_in 'Title', with: post.title
fill_in 'Body', with: post.body
click_button 'Create Post'
end
This will redirect_to post_path(post)
views/posts/index.html.erb
<%= form_tag(posts_path, method: :get, class: "block") do %>
<div class="form-group">
<div class="input-group">
<%= text_field_tag :search, params[:search], class: "form-control", id: "search" %>
<span class="input-group-btn">
<%= submit_tag "Search", name: nil, class: "btn btn-default" %>
</span>
</div>
</div>
<% end %>
Capybara output
Failure/Error: fill_in "search", with: post3.title
Capybara::ElementNotFound:
Unable to find field "search"

Answer 1

The command fill_in "search", with: post3.title you're using should work, assuming you are on the page rendering the shown partial, and the output of that partial is actually visible on the page (not hidden via CSS). Your scenario doesn't show visiting an actual page, and you don't show what fill_post_form is doing so it's tough to know exactly what is going wrong. First step would be to do something like
fill_post_form(post3) # already in your tests
sleep 2 # wait a few seconds to make sure above method has completed whatever actions it does
puts page.html # output the current page and take a look to see if your 'search' element is actually on the page