use json as default response format

config/routes.rb

@@ -1,5 +1,7 @@
 Rails.application.routes.draw do
-  resources :posts, only: [:index, :show, :create]
-  resources :user_follows, only: [:create, :destroy]
-  resources :users, only: [:show]
+  defaults format: :json do
+    resources :posts, only: [:index, :show, :create]
+    resources :user_follows, only: [:create, :destroy]
+    resources :users, only: [:show]
+  end
 end

spec/routing/posts_routing_spec.rb

@@ -3,16 +3,16 @@ require "rails_helper"
 RSpec.describe PostsController, type: :routing do
   describe "routing" do
     it "routes to #index" do
-      expect(get: "/posts").to route_to("posts#index")
+      expect(get: "/posts").to route_to("posts#index", format: :json)
     end
 
     it "routes to #show" do
-      expect(get: "/posts/1").to route_to("posts#show", id: "1")
+      expect(get: "/posts/1").to route_to("posts#show", id: "1", format: :json)
     end
 
 
     it "routes to #create" do
-      expect(post: "/posts").to route_to("posts#create")
+      expect(post: "/posts").to route_to("posts#create", format: :json)
     end
   end
 end

spec/routing/user_follows_routing_spec.rb

@@ -3,11 +3,11 @@ require "rails_helper"
 RSpec.describe UserFollowsController, type: :routing do
   describe "routing" do
     it "routes to #create" do
-      expect(post: "/user_follows").to route_to("user_follows#create")
+      expect(post: "/user_follows").to route_to("user_follows#create", format: :json)
     end
 
     it "routes to #destroy" do
-      expect(delete: "/user_follows/1").to route_to("user_follows#destroy", id: "1")
+      expect(delete: "/user_follows/1").to route_to("user_follows#destroy", id: "1", format: :json)
     end
   end
 end

spec/routing/users_routing_spec.rb

@@ -3,7 +3,7 @@ require "rails_helper"
 RSpec.describe UsersController, type: :routing do
   describe "routing" do
     it "routes to #show" do
-      expect(get: "/users/1").to route_to("users#show", id: "1")
+      expect(get: "/users/1").to route_to("users#show", id: "1", format: :json)
     end
   end
 end