diff --git a/Library/Homebrew/build_options.rb b/Library/Homebrew/build_options.rb
index 0cd3a5a467..441a81bc29 100644
--- a/Library/Homebrew/build_options.rb
+++ b/Library/Homebrew/build_options.rb
@@ -100,13 +100,26 @@ class BuildOptions
   # implicit_options are needed because `depends_on 'spam' => 'with-stuff'`
   # complains if 'spam' has stuff as default and only defines `--without-stuff`.
   def implicit_options
-    implicit = unused_options.map do |o|
-      if o.name =~ /^with-(.+)$/ && without?($1)
-        Option.new("without-#{$1}")  # we lose the description, but that's ok
-      elsif o.name =~ /^without-(.+)$/ && with?($1)
-        Option.new("with-#{$1}")
-      end
+    implicit = unused_options.map do |option|
+      opposite_of option unless has_opposite_of? option
     end.compact
     Options.new(implicit)
   end
+
+  def has_opposite_of? option
+    true if args.include? opposite_of option
+  end
+
+  def opposite_of option
+    option = Option.new option
+    if option.name =~ /^with-(.+)$/
+      Option.new("without-#{$1}")
+    elsif option.name =~ /^without-(.+)$/
+      Option.new("with-#{$1}")
+    elsif option.name =~ /^enable-(.+)$/
+      Option.new("disable-#{$1}")
+    elsif option.name =~ /^disable-(.+)$/
+      Option.new("enable-#{$1}")
+    end
+  end
 end
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index 39bea8ee68..e5b071c0f3 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -515,6 +515,9 @@ class Formula
   def test
     require 'test/unit/assertions'
     extend(Test::Unit::Assertions)
+    # Adding the used options allows us to use `build.with?` inside of tests
+    tab = Tab.for_name(name)
+    tab.used_options.each { |opt| build.args << opt unless build.has_opposite_of? opt }
     ret = nil
     mktemp do
       @testpath = Pathname.pwd
diff --git a/Library/Homebrew/python_helper.rb b/Library/Homebrew/python_helper.rb
index 8ebf0b7943..bace441fc0 100644
--- a/Library/Homebrew/python_helper.rb
+++ b/Library/Homebrew/python_helper.rb
@@ -16,11 +16,11 @@
 def python_helper(options={:allowed_major_versions => [2, 3]}, &block)
   if !block_given? and !@current_python.nil?
     # We are already inside of a `python do ... end` block, so just return
-    # the current_python or false if the version.major is not allowed.
+    # the current_python or nil if the version.major is not allowed.
     if options[:allowed_major_versions].include?(@current_python.version.major)
       return @current_python
     else
-      return false
+      return nil
     end
   end
 
@@ -42,7 +42,7 @@ def python_helper(options={:allowed_major_versions => [2, 3]}, &block)
   end
 
   # Allow to use an else-branch like so: `if python do ... end; else ... end`.
-  return false if filtered_python_reqs.empty?
+  return nil if filtered_python_reqs.empty?
 
   # Sort by version, so the older 2.x will be used first and if no
   # block_given? then 2.x is preferred because it is returned.
diff --git a/Library/Homebrew/test/test_build_options.rb b/Library/Homebrew/test/test_build_options.rb
index cc5fd01d7b..9e2a9e06f0 100644
--- a/Library/Homebrew/test/test_build_options.rb
+++ b/Library/Homebrew/test/test_build_options.rb
@@ -1,9 +1,9 @@
-require 'testing_env'
+  require 'testing_env'
 require 'build_options'
 
 class BuildOptionsTests < Test::Unit::TestCase
   def setup
-    args = %w{--with-foo --with-bar --without-qux}
+    args = %w{--with-foo --with-bar --without-qux} # args fake the command line
     @build = BuildOptions.new(args)
     @build.add("with-foo")
     @build.add("with-bar")
@@ -44,7 +44,7 @@ class BuildOptionsTests < Test::Unit::TestCase
   end
 
   def test_implicit_options
-    # --without-baz is not explicitly specified on the command line
+    # --without-baz is not explicitly specified on the command line (i.e. args)
     # therefore --with-baz should be implicitly assumed:
     assert @build.implicit_options.include?("--with-baz")
     # But all these should not be in the implict_options:
@@ -53,4 +53,18 @@ class BuildOptionsTests < Test::Unit::TestCase
     assert !@build.implicit_options.include?("--without-bar")
     assert !@build.implicit_options.include?("--with-qux")
   end
+
+  def test_opposite_of
+    assert @build.opposite_of(Option.new("with-foo")) == Option.new("without-foo")
+    assert @build.opposite_of("without-foo") == Option.new("with-foo")
+    assert @build.opposite_of(Option.new("enable-spam")) == Option.new("disable-spam")
+    assert @build.opposite_of("disable-beer") == Option.new("enable-beer")
+  end
+
+  def test_has_opposite_of?
+    assert @build.has_opposite_of?("--without-foo")
+    assert @build.has_opposite_of?(Option.new("--with-qux"))
+    assert !@build.has_opposite_of?("--without-qux")
+    assert !@build.has_opposite_of?("--without-nonexisting")
+  end
 end