Create facade for switching assertion libraries

This is in preparation of requiring different testing libraries based on
the rails version.

Author: vanstee

lib/rspec/rails/adapters.rb

@@ -1,14 +1,18 @@
 require 'delegate'
 require 'active_support/concern'
-require 'test/unit/assertions'
 
 module RSpec
   module Rails
+    module Assertions
+      require 'test/unit/assertions'
+      include Test::Unit::Assertions
+    end
+
     class AssertionDelegator < Module
       # @api private
       def initialize(*assertion_modules)
         assertion_class = Class.new(SimpleDelegator) do
-          include Test::Unit::Assertions
+          include ::RSpec::Rails::Assertions
           include ::RSpec::Rails::MinitestCounters
           assertion_modules.each { |mod| include mod }
         end
@@ -122,7 +126,7 @@ module ClassMethods
         # examples without exposing non-assertion methods in Test::Unit or
         # Minitest.
         def assertion_method_names
-          Test::Unit::Assertions.public_instance_methods.select{|m| m.to_s =~ /^(assert|flunk)/} +
+          ::RSpec::Rails::Assertions.public_instance_methods.select{|m| m.to_s =~ /^(assert|flunk)/} +
             [:build_message]
         end
 
@@ -139,7 +143,7 @@ def #{m}(*args, &block)
       end
 
       class AssertionDelegator
-        include Test::Unit::Assertions
+        include ::RSpec::Rails::Assertions
         include ::RSpec::Rails::MinitestCounters
       end
 

spec/rspec/rails/assertion_adapter_spec.rb

@@ -3,7 +3,7 @@
 describe RSpec::Rails::TestUnitAssertionAdapter do
   include RSpec::Rails::TestUnitAssertionAdapter
 
-  Test::Unit::Assertions.public_instance_methods.select{|m| m.to_s =~ /^(assert|flunk)/}.each do |m|
+  RSpec::Rails::Assertions.public_instance_methods.select{|m| m.to_s =~ /^(assert|flunk)/}.each do |m|
     if m.to_s == "assert_equal"
       it "exposes #{m} to host examples" do
         assert_equal 3,3

spec/rspec/rails/assertion_delegator_spec.rb

@@ -3,7 +3,7 @@
 describe RSpec::Rails::AssertionDelegator do
   it "provides a module that delegates assertion methods to an isolated class" do
     klass = Class.new {
-      include RSpec::Rails::AssertionDelegator.new(Test::Unit::Assertions)
+      include RSpec::Rails::AssertionDelegator.new(RSpec::Rails::Assertions)
     }
 
     expect(klass.new).to respond_to(:assert)

spec/rspec/rails/mocks/mock_model_spec.rb

@@ -360,7 +360,6 @@
   end
 
   describe "ActiveModel Lint tests" do
-    require 'test/unit/assertions'
     require 'active_model/lint'
     include RSpec::Rails::TestUnitAssertionAdapter
     include ActiveModel::Lint::Tests