render_template matcher
The render_template matcher is used to specify that a request renders a
  given template or layout.  It delegates to
  assert_template
It is available in controller specs (spec/controllers) and request specs (spec/requests).
NOTE: use redirect_to(:action => 'new') for redirects, not render_template.
Using render_template with three possible options
Given a file named “spec/controllers/gadgets_spec.rb” with:
require "rails_helper"
RSpec.describe GadgetsController , type: :controller do
  describe "GET #index" do
    subject { get :index }
    it "renders the index template" do
      expect(subject).to render_template(:index)
      expect(subject).to render_template("index")
      expect(subject).to render_template("gadgets/index")
    end
    it "does not render a different template" do
      expect(subject).to_not render_template("gadgets/show")
    end
  end
end
When I run rspec spec/controllers/gadgets_spec.rb
Then the examples should all pass.
Specify that a request renders a given layout
Given a file named “spec/controllers/gadgets_spec.rb” with:
require "rails_helper"
RSpec.describe GadgetsController , type: :controller do
  describe "GET #index" do
    subject { get :index }
    it "renders the application layout" do
      expect(subject).to render_template("layouts/application")
    end
    it "does not render a different layout" do
      expect(subject).to_not render_template("layouts/admin")
    end
  end
end
When I run rspec spec/controllers/gadgets_spec.rb
Then the examples should all pass.
Using render_template in a view spec
Given a file named “spec/views/gadgets/index.html.erb_spec.rb” with:
require "rails_helper"
RSpec.describe "gadgets/index" , type: :view do
  it "renders the index template" do
    assign(:gadgets, [Gadget.create!])
    render
    expect(view).to render_template(:index)
    expect(view).to render_template("index")
    expect(view).to render_template("gadgets/index")
  end
  it "does not render a different template" do
    expect(view).to_not render_template("gadgets/show")
  end
end
When I run rspec spec/views
Then the examples should all pass.