Run tests for both build environments

Library/Homebrew/test/test_ENV.rb

 require 'testing_env'
 require 'extend/ENV'
 
-class EnvironmentTests < Homebrew::TestCase
+module SharedEnvTests
   def setup
     @env = {}.extend(EnvActivation)
-    @env.activate_extensions!
   end
 
   def test_switching_compilers
@@ -105,9 +104,7 @@ class EnvironmentTests < Homebrew::TestCase
     @env.prepend_path 'FOO', '/bin'
     assert_equal "/bin#{File::PATH_SEPARATOR}/usr/bin", @env['FOO']
   end
-end
 
-module SharedEnvTests
   def test_switching_compilers_updates_compiler
     [:clang, :llvm, :gcc, :gcc_4_0].each do |compiler|
       @env.send(compiler)
@@ -128,7 +125,8 @@ class StdenvTests < Homebrew::TestCase
   include SharedEnvTests
 
   def setup
-    @env = {}.extend(Stdenv)
+    super
+    @env.extend(Stdenv)
   end
 end
 
@@ -136,7 +134,8 @@ class SuperenvTests < Homebrew::TestCase
   include SharedEnvTests
 
   def setup
-    @env = {}.extend(Superenv)
+    super
+    @env.extend(Superenv)
   end
 
   def test_initializes_deps