fix brittle URI parser tests failing on Rubinius

The tests relied on the output of Method#to_s, which seems unreliable on
non-MRI Rubies. Avoid that and ensure the default_uri_parser is restored.

test/utils_test.rb

@@ -5,10 +5,6 @@ class TestUtils < Faraday::TestCase
     @url = "http://example.com/abc"
   end
 
-  def teardown
-    Faraday::Utils.default_uri_parser = nil
-  end
-
   # emulates ActiveSupport::SafeBuffer#gsub
   FakeSafeBuffer = Struct.new(:string) do
     def to_s() self end
@@ -26,28 +22,37 @@ class TestUtils < Faraday::TestCase
   end
 
   def test_parses_with_default
-    assert_equal %(#<Method: Kernel.URI>), Faraday::Utils.default_uri_parser.to_s
+    with_default_uri_parser(nil) do
       uri = normalize(@url)
       assert_equal 'example.com', uri.host
     end
+  end
 
   def test_parses_with_URI
-    Faraday::Utils.default_uri_parser = ::URI
+    with_default_uri_parser(::URI) do
-    assert_equal %(#<Method: URI.parse>), Faraday::Utils.default_uri_parser.to_s
       uri = normalize(@url)
       assert_equal 'example.com', uri.host
     end
-
-  def test_parses_with_block
-    Faraday::Utils.default_uri_parser = lambda do |uri|
-      "booya#{"!" * uri.size}"
   end
 
+  def test_parses_with_block
+    with_default_uri_parser(lambda {|u| "booya#{"!" * u.size}" }) do
       assert_equal 'booya!!!!!!!!!!!!!!!!!!!!!!', normalize(@url)
     end
+  end
 
   def normalize(url)
     Faraday::Utils::URI(url)
   end
+
+  def with_default_uri_parser(parser)
+    old_parser = Faraday::Utils.default_uri_parser
+    begin
+      Faraday::Utils.default_uri_parser = parser
+      yield
+    ensure
+      Faraday::Utils.default_uri_parser = old_parser
+    end
+  end
 end