Use dedicated methods for memoized values (#1211)

RuboCop didn't seem to like having memoization in the
`default_constants` method that didn't match the method name. This
satisfies RuboCop, and saves us an array allocation or two when we run
specs that don't use any of these helpers.

.rubocop.yml

@@ -76,11 +76,6 @@ Metrics/BlockLength:
 Metrics/LineLength:
   Max: 189
 
-# Offense count: 1
-Naming/MemoizedInstanceVariableName:
-  Exclude:
-    - 'spec/support/macros/define_constant.rb'
-
 # Offense count: 3
 # Cop supports --auto-correct.
 # Configuration parameters: EnforcedStyle, ProceduralMethods, FunctionalMethods, IgnoredMethods.

spec/support/macros/define_constant.rb

@@ -6,7 +6,7 @@ module DefineConstantMacros
     klass = Class.new(base)
     namespace.const_set(class_name, klass)
     klass.class_eval(&block) if block_given?
-    @defined_constants << path
+    defined_constants << path
     klass
   end
 
@@ -26,7 +26,7 @@ module DefineConstantMacros
     begin
       connection.execute("DROP TABLE IF EXISTS #{table_name}")
       connection.create_table(table_name, &block)
-      @created_tables << table_name
+      created_tables << table_name
       connection
     rescue Exception => exception
       connection.execute("DROP TABLE IF EXISTS #{table_name}")
@@ -41,27 +41,32 @@ module DefineConstantMacros
     [namespace, class_name]
   end
 
-  def default_constants
-    @defined_constants ||= []
-    @created_tables    ||= []
-  end
-
   def clear_generated_constants
-    @defined_constants.reverse.each do |path|
+    defined_constants.reverse.each do |path|
       namespace, class_name = *constant_path(path)
       namespace.send(:remove_const, class_name)
     end
 
-    @defined_constants.clear
+    defined_constants.clear
   end
 
   def clear_generated_tables
-    @created_tables.each do |table_name|
+    created_tables.each do |table_name|
       ActiveRecord::Base.
         connection.
         execute("DROP TABLE IF EXISTS #{table_name}")
     end
-    @created_tables.clear
+    created_tables.clear
+  end
+
+  private
+
+  def defined_constants
+    @defined_constants ||= []
+  end
+
+  def created_tables
+    @created_tables ||= []
   end
 end
 
@@ -75,10 +80,6 @@ RSpec.configure do |config|
     )
   end
 
-  config.before do
-    default_constants
-  end
-
   config.after do
     clear_generated_constants
     clear_generated_tables