Improve test setup and teardown

Author: rmosolgo

spec/graphql/schema/visibility_spec.rb

@@ -312,7 +312,10 @@ def self.resolve_type(...); Thing; end
   end
 
   it "defaults to preload: true for Rails.env.staging?" do
-    prev_rails = defined?(Rails) ? Rails : nil
+    if defined?(Rails)
+      prev_rails = Rails
+      Object.send :remove_const, :Rails
+    end
     mock_env = OpenStruct.new(:staging? => true)
     Object.const_set(:Rails, OpenStruct.new(env: mock_env))
     schema = Class.new(GraphQL::Schema) do
@@ -331,8 +334,9 @@ def self.resolve_type(...); Thing; end
     refute Rails.env.staging?
     refute schema.visibility.preload?
   ensure
+    Object.send(:remove_const, :Rails)
     if prev_rails
-      const_set(:Rails, prev_rails)
+      Object.const_set(:Rails, prev_rails)
     end
   end
 end