More robust way to avoid attempting to marshal Procs

Library/Homebrew/formula.rb

@@ -26,7 +26,6 @@ class Formula
     set_instance_variable :bottle
     set_instance_variable :devel
     set_instance_variable :head
-    set_instance_variable :test
 
     @name = name
     validate_variable :name
@@ -591,14 +590,14 @@ public
     ret = nil
     mktemp do
       @testpath = Pathname.pwd
-      ret = instance_eval(&@test)
+      ret = instance_eval(&self.class.test)
       @testpath = nil
     end
     ret
   end
 
   def test_defined?
-    not @test.nil?
+    not self.class.instance_variable_get(:@test_defined).nil?
   end
 
 private
@@ -651,7 +650,7 @@ private
     when :brew
       raise "You cannot override Formula#brew"
     when :test
-      @test = method
+      @test_defined = true
     end
   end
 
@@ -800,11 +799,8 @@ private
 
     def test &block
       return @test unless block_given?
-      # If this formula is the executing script, we are performing an
-      # install. Since it may be marshalled back to the main process as
-      # part of an exception, don't store this Proc because Procs can't
-      # be marshalled.
-      @test = block unless $0 != HOMEBREW_BREW_FILE.to_s
+      @test_defined = true
+      @test = block
     end
   end
 end