Use explicit checks instead of custom matcher.

Library/Homebrew/cask/spec/cask/artifact/binary_spec.rb

@@ -20,7 +20,8 @@ describe Hbc::Artifact::Binary do
     shutup do
       Hbc::Artifact::Binary.new(cask).install_phase
     end
-    expect(expected_path).to be_a_valid_symlink
+    expect(expected_path).to be_a_symlink
+    expect(expected_path.readlink).to exist
   end
 
   it "avoids clobbering an existing binary by linking over it" do
@@ -82,7 +83,8 @@ describe Hbc::Artifact::Binary do
         Hbc::Artifact::Binary.new(cask).install_phase
       end
 
-      expect(expected_path).to be_a_valid_symlink
+      expect(expected_path).to be_a_symlink
+      expect(expected_path.readlink).to exist
     end
   end
 end

Library/Homebrew/cask/spec/spec_helper.rb

@@ -34,5 +34,4 @@ end
 RSpec.configure do |config|
   config.order = :random
   config.include(Test::Helper::Shutup)
-  config.include(FileMatchers)
 end

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

-module FileMatchers
-  extend RSpec::Matchers::DSL
-
-  matcher :be_a_valid_symlink do
-    match do |path|
-      path.symlink? && path.readlink.exist?
-    end
-  end
-end