Move `vendor/bundle` up one level to `HOMEBREW_LIBRARY_PATH`.

Library/Homebrew/cask/Gemfile.lock

@@ -26,7 +26,7 @@ GEM
     metaclass (0.0.4)
     method_source (0.8.2)
     minitest (5.9.1)
-    minitest-reporters (1.1.11)
+    minitest-reporters (1.1.12)
       ansi
       builder
       minitest (>= 5.0)

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

 require "English"
 
+ENV["BUNDLE_GEMFILE"] = "#{HOMEBREW_LIBRARY_PATH}/cask/Gemfile"
+ENV["BUNDLE_PATH"] = "#{HOMEBREW_LIBRARY_PATH}/vendor/bundle"
+
 def run_tests(executable, files, args = [])
   opts = []
   opts << "--serialize-stdout" if ENV["CI"]
@@ -7,7 +10,7 @@ def run_tests(executable, files, args = [])
   system "bundle", "exec", executable, *opts, "--", *args, "--", *files
 end
 
-repo_root = Pathname(__FILE__).realpath.parent.parent
+repo_root = Pathname.new(__FILE__).realpath.parent.parent
 repo_root.cd do
   ENV["HOMEBREW_NO_ANALYTICS_THIS_RUN"] = "1"
   ENV["HOMEBREW_NO_EMOJI"] = "1"
@@ -15,7 +18,7 @@ repo_root.cd do
 
   Homebrew.install_gem_setup_path! "bundler"
   unless quiet_system("bundle", "check")
-    system "bundle", "install", "--path", "vendor/bundle"
+    system "bundle", "install"
   end
 
   rspec = ARGV.flag?("--rspec") || !ARGV.flag?("--minitest")

Library/Homebrew/dev-cmd/tests.rb

@@ -26,7 +26,8 @@ module Homebrew
         FileUtils.rm_f "test/coverage/.resultset.json"
       end
 
-      ENV["BUNDLE_GEMFILE"] = "#{Dir.pwd}/test/Gemfile"
+      ENV["BUNDLE_GEMFILE"] = "#{HOMEBREW_LIBRARY_PATH}/test/Gemfile"
+      ENV["BUNDLE_PATH"] = "#{HOMEBREW_LIBRARY_PATH}/vendor/bundle"
 
       # Override author/committer as global settings might be invalid and thus
       # will cause silent failure during the setup of dummy Git repositories.
@@ -37,7 +38,7 @@ module Homebrew
 
       Homebrew.install_gem_setup_path! "bundler"
       unless quiet_system("bundle", "check")
-        system "bundle", "install", "--path", "vendor/bundle"
+        system "bundle", "install"
       end
 
       # Make it easier to reproduce test runs.

Library/Homebrew/test/Gemfile

@@ -13,7 +13,8 @@ group :coverage do
   #  - https://github.com/colszowka/simplecov/pull/520
   gem "simplecov", "0.12.0",
     git: "https://github.com/colszowka/simplecov.git",
-    branch: "master", # commit 83d8031ddde0927f87ef9327200a98583ca18d77
+    branch: "master",
+    ref: "83d8031ddde0927f87ef9327200a98583ca18d77",
     require: false
   gem "codecov", require: false
 end

Library/Homebrew/test/Gemfile.lock

 GIT
   remote: https://github.com/colszowka/simplecov.git
   revision: 83d8031ddde0927f87ef9327200a98583ca18d77
+  ref: 83d8031ddde0927f87ef9327200a98583ca18d77
   branch: master
   specs:
     simplecov (0.12.0)
@@ -11,18 +12,18 @@ GIT
 GEM
   remote: https://rubygems.org/
   specs:
-    codecov (0.1.5)
+    codecov (0.1.6)
       json
       simplecov
       url
     docile (1.1.5)
-    json (1.8.3)
+    json (2.0.2)
     metaclass (0.0.4)
-    minitest (5.9.0)
-    mocha (1.1.0)
+    minitest (5.9.1)
+    mocha (1.2.1)
       metaclass (~> 0.0.1)
     parallel (1.9.0)
-    parallel_tests (2.9.0)
+    parallel_tests (2.10.0)
       parallel
     rake (10.5.0)
     simplecov-html (0.10.0)
@@ -40,4 +41,4 @@ DEPENDENCIES
   simplecov (= 0.12.0)!
 
 BUNDLED WITH
-   1.13.1
+   1.13.6