diff --git a/Library/Homebrew/test/audit_test.rb b/Library/Homebrew/test/audit_test.rb
index f8d13748223e48f107c3c2fcd4253a8cee5ea0e7..75a882d6934af7a44ef78aa07e5bcf480ceb5034 100644
--- a/Library/Homebrew/test/audit_test.rb
+++ b/Library/Homebrew/test/audit_test.rb
@@ -361,13 +361,10 @@ class FormulaAuditorTests < Homebrew::TestCase
       end
     EOS
 
-    original_value = ENV["HOMEBREW_NO_GITHUB_API"]
     ENV["HOMEBREW_NO_GITHUB_API"] = "1"
 
     fa.audit_github_repository
     assert_equal [], fa.problems
-  ensure
-    ENV["HOMEBREW_NO_GITHUB_API"] = original_value
   end
 
   def test_audit_caveats
diff --git a/Library/Homebrew/test/commands_test.rb b/Library/Homebrew/test/commands_test.rb
index 3d7c16e58fbe26188c379e885de97596ffe98194..5f5dc95865af1a32009bd36573cf2fd995a6456d 100644
--- a/Library/Homebrew/test/commands_test.rb
+++ b/Library/Homebrew/test/commands_test.rb
@@ -47,8 +47,6 @@ class CommandsTests < Homebrew::TestCase
   end
 
   def test_external_commands
-    env = ENV.to_hash
-
     mktmpdir do |dir|
       %w[brew-t1 brew-t2.rb brew-t3.py].each do |file|
         path = "#{dir}/#{file}"
@@ -67,8 +65,6 @@ class CommandsTests < Homebrew::TestCase
         "Executable files with a non Ruby extension shoudn't be included"
       refute cmds.include?("t4"), "Non-executable files shouldn't be included"
     end
-  ensure
-    ENV.replace(env)
   end
 
   def test_internal_command_path
diff --git a/Library/Homebrew/test/diagnostic_test.rb b/Library/Homebrew/test/diagnostic_test.rb
index 2d12868273febb04bf9a732f3bbb6d85c4c76013..7a1fb25f7930bc4a4f7c7b213fcc72342272d859 100644
--- a/Library/Homebrew/test/diagnostic_test.rb
+++ b/Library/Homebrew/test/diagnostic_test.rb
@@ -6,15 +6,9 @@ require "diagnostic"
 class DiagnosticChecksTest < Homebrew::TestCase
   def setup
     super
-    @env = ENV.to_hash
     @checks = Homebrew::Diagnostic::Checks.new
   end
 
-  def teardown
-    ENV.replace(@env)
-    super
-  end
-
   def test_inject_file_list
     assert_equal "foo:\n",
       @checks.inject_file_list([], "foo:\n")
diff --git a/Library/Homebrew/test/os/mac/diagnostic_test.rb b/Library/Homebrew/test/os/mac/diagnostic_test.rb
index 284d293ca939c128adeec8545a5793d600445273..5f467e87be2420edb21cb9285c849ef88eda1d53 100644
--- a/Library/Homebrew/test/os/mac/diagnostic_test.rb
+++ b/Library/Homebrew/test/os/mac/diagnostic_test.rb
@@ -6,15 +6,9 @@ require "diagnostic"
 class OSMacDiagnosticChecksTest < Homebrew::TestCase
   def setup
     super
-    @env = ENV.to_hash
     @checks = Homebrew::Diagnostic::Checks.new
   end
 
-  def teardown
-    ENV.replace(@env)
-    super
-  end
-
   def test_check_for_other_package_managers
     MacOS.stubs(:macports_or_fink).returns ["fink"]
     assert_match "You have MacPorts or Fink installed:",
diff --git a/Library/Homebrew/test/shell_test.rb b/Library/Homebrew/test/shell_test.rb
index 877acb5c8b9747594ea2d44428021390ac334d91..a32d09863816c7247297dada7ae3630da344fc2f 100644
--- a/Library/Homebrew/test/shell_test.rb
+++ b/Library/Homebrew/test/shell_test.rb
@@ -37,7 +37,6 @@ class ShellSmokeTest < Homebrew::TestCase
   end
 
   def prepend_path_shell(shell, path, fragment)
-    original_shell = ENV["SHELL"]
     ENV["SHELL"] = shell
 
     prepend_message = Utils::Shell.prepend_path_in_shell_profile(path)
@@ -45,8 +44,6 @@ class ShellSmokeTest < Homebrew::TestCase
       prepend_message.start_with?(fragment),
       "#{shell}: expected #{prepend_message} to match #{fragment}"
     )
-
-    ENV["SHELL"] = original_shell
   end
 
   def test_prepend_path_in_shell_profile
diff --git a/Library/Homebrew/test/support/helper/test_case.rb b/Library/Homebrew/test/support/helper/test_case.rb
index 53d4e70317936cce4aee8099eaa2aef58792fb15..c4c7f872752b16875094a00d11245f2ff28e04fd 100644
--- a/Library/Homebrew/test/support/helper/test_case.rb
+++ b/Library/Homebrew/test/support/helper/test_case.rb
@@ -16,11 +16,14 @@ module Homebrew
 
     def setup
       super
+
       @__argv = ARGV.dup
+      @__env = copy_env # Call #to_hash to duplicate ENV
     end
 
     def teardown
       ARGV.replace(@__argv)
+      restore_env @__env
 
       Tab.clear_cache
 
diff --git a/Library/Homebrew/test/utils_test.rb b/Library/Homebrew/test/utils_test.rb
index 7099e332c22cfe3bd2e8ecb43ba9e52df99462b7..7ff4e192ac74fbe8d8dcfa26c4fa8d11f623446e 100644
--- a/Library/Homebrew/test/utils_test.rb
+++ b/Library/Homebrew/test/utils_test.rb
@@ -7,12 +7,6 @@ class UtilTests < Homebrew::TestCase
   def setup
     super
     @dir = Pathname.new(mktmpdir)
-    @env = ENV.to_hash
-  end
-
-  def teardown
-    ENV.replace @env
-    super
   end
 
   def test_ofail