cask/spec: replace with_env_var with with_environment

Library/Homebrew/cask/spec/cask/cli_spec.rb

@@ -41,14 +41,14 @@ describe Hbc::CLI do
     end
 
     it "respects the env variable when choosing what appdir to create" do
-      EnvHelper.with_env_var("HOMEBREW_CASK_OPTS", "--appdir=/custom/appdir") do
+      with_environment "HOMEBREW_CASK_OPTS" => "--appdir=/custom/appdir" do
         expect(Hbc).to receive(:appdir=).with(Pathname("/custom/appdir"))
         described_class.process("noop")
       end
     end
 
     it "respects the env variable when choosing a non-default Caskroom location" do
-      EnvHelper.with_env_var "HOMEBREW_CASK_OPTS", "--caskroom=/custom/caskdir" do
+      with_environment "HOMEBREW_CASK_OPTS" => "--caskroom=/custom/caskdir" do
         expect(Hbc).to receive(:caskroom=).with(Pathname("/custom/caskdir"))
         described_class.process("noop")
       end

Library/Homebrew/cask/spec/spec_helper.rb

@@ -16,6 +16,7 @@ require "global"
 # add Homebrew-Cask to load path
 $LOAD_PATH.push(project_root.join("lib").to_s)
 
+require "test/helper/env"
 require "test/helper/shutup"
 
 Dir["#{project_root}/spec/support/*.rb"].each(&method(:require))
@@ -61,5 +62,6 @@ Hbc.caskroom = Hbc.homebrew_prefix.join("TestCaskroom")
 
 RSpec.configure do |config|
   config.order = :random
+  config.include(Test::Helper::Env)
   config.include(Test::Helper::Shutup)
 end

Library/Homebrew/cask/spec/support/env_helper.rb

-module EnvHelper
-  class << self
-    def with_env_var(key, val)
-      was_defined = ENV.key? "key"
-      old_value = ENV["key"]
-      ENV[key] = val
-      yield
-    ensure
-      if was_defined
-        ENV[key] = old_value
-      else
-        ENV.delete(key)
-      end
-    end
-  end
-end