new error scheme for CreateUser and Interactors generally

app/interactors/create_user.rb

@@ -1,6 +1,6 @@
 class CreateUser < StandardInteraction
-  def validate_input
-    context.fail!(errors: "invalid user params") unless context.user_params
+  def validate_input(input: :user_params)
+    super
   end
 
   def execute

lib/standard_interaction.rb

@@ -10,9 +10,14 @@ def call
   def execute
   end
 
-  def validate_input
+  def validate_input(input: expected_arguments)
+    context.fail!(errors: input_error) unless context.send(input)
   end
 
   def validate_output
   end
+
+  def input_error
+    { "#{self.class.name}": "invalid Interactor input" }
+  end
 end

spec/interactors/create_user_spec.rb

@@ -52,7 +52,7 @@
       end
 
       it "returns an error" do
-        expect(subject.errors).to eq("invalid user params")
+        expect(subject.errors).to eq(CreateUser: "invalid Interactor input")
       end
     end
   end