Convert brew cask test to spec.

Library/Homebrew/test/cask_test.rb

@@ -1,10 +0,0 @@
-require "testing_env"
-
-class IntegrationCommandTestCask < IntegrationCommandTestCase
-  def test_cask
-    needs_test_cmd_taps
-    needs_macos
-    setup_remote_tap("caskroom/cask")
-    cmd("cask", "list", "--caskroom=#{HOMEBREW_PREFIX}/Caskroom")
-  end
-end

Library/Homebrew/test/cmd/cask_spec.rb

@@ -0,0 +1,8 @@
+describe "brew cask", :integration_test, :needs_macos, :needs_official_cmd_taps do
+  describe "list" do
+    it "returns a list of installed Casks" do
+      setup_remote_tap("caskroom/cask")
+      expect { brew "cask", "list" }.to be_a_success
+    end
+  end
+end