Merge pull request #1008 from libgit2/cmn/freeze-test-string

test: avoid modifying our test string

Author: carlosmn

test/diff_test.rb

@@ -1145,9 +1145,7 @@ def test_patch
 \\ No newline at end of file
 EOS
 
-    expected.force_encoding('binary') if expected.respond_to?(:force_encoding)
-
-    assert_equal expected, diff.patch
+    assert_equal expected.b, diff.patch
   end
 
   def test_patch_compact