Set `HOMEBREW_NO_EMOJI` and `HOMEBREW_CASK_OPTS` in `cask-tests`.

Library/Homebrew/cask/cmd/brew-cask-tests.rb

@@ -10,6 +10,8 @@ end
 repo_root = Pathname(__FILE__).realpath.parent.parent
 repo_root.cd do
   ENV["HOMEBREW_NO_ANALYTICS_THIS_RUN"] = "1"
+  ENV["HOMEBREW_NO_EMOJI"] = "1"
+  ENV.delete("HOMEBREW_CASK_OPTS")
 
   Homebrew.install_gem_setup_path! "bundler"
   unless quiet_system("bundle", "check")

Library/Homebrew/cask/spec/spec_helper.rb

@@ -16,10 +16,6 @@ require "global"
 # add Homebrew-Cask to load path
 $LOAD_PATH.push(project_root.join("lib").to_s)
 
-# force some environment variables
-ENV["HOMEBREW_NO_EMOJI"] = "1"
-ENV["HOMEBREW_CASK_OPTS"] = nil
-
 require "test/helper/shutup"
 
 Dir["#{project_root}/spec/support/*.rb"].each(&method(:require))

Library/Homebrew/cask/test/test_helper.rb

@@ -17,10 +17,6 @@ require "global"
 # add Homebrew-Cask to load path
 $LOAD_PATH.push(project_root.join("lib").to_s)
 
-# force some environment variables
-ENV["HOMEBREW_NO_EMOJI"] = "1"
-ENV["HOMEBREW_CASK_OPTS"] = nil
-
 require "test/helper/shutup"
 include Test::Helper::Shutup