Remain V3 endpoint unchanged

lib/api/api.rb

 module API
   class API < Grape::API
     include APIGuard
-    version 'v3', using: :path
+
+    version %w(v3 v4), using: :path
+
+    version 'v3', using: :path do
+      mount ::API::V3::Projects
+    end
 
     before { allow_access_with_scope :api }
 

spec/support/api_helpers.rb

@@ -17,8 +17,8 @@ module ApiHelpers
   #   => "/api/v2/issues?foo=bar&private_token=..."
   #
   # Returns the relative path to the requested API resource
-  def api(path, user = nil)
-    "/api/#{API::API.version}#{path}" +
+  def api(path, user = nil, version: API::API.version)
+    "/api/#{version}#{path}" +
 
       # Normalize query string
       (path.index('?') ? '' : '?') +
@@ -31,6 +31,11 @@ module ApiHelpers
       end
   end
 
+  # Temporary helper method for simplifying V3 exclusive API specs
+  def v3_api(path, user = nil)
+    api(path, user, version: 'v3')
+  end
+
   def ci_api(path, user = nil)
     "/ci/api/v1/#{path}" +