Add unit test for parameterized strings.

test/fixtures/strings-3.txt

@@ -0,0 +1,5 @@
+[[My Strings]]
+    [parameterized_string]
+        en = The %@ brown fox jumps over the %@ dog %d times.
+    [percentage_string]
+        en = This product is %d%% off.

test/fixtures/test-output-8.txt

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!-- Android Strings File -->
+<!-- Generated by Twine <%= Twine::VERSION %> -->
+<!-- Language: en -->
+<resources>
+	<!-- SECTION: My Strings -->
+	<string name="parameterized_string">The %1$s brown fox jumps over the %2$s dog %3$d times.</string>
+	<string name="percentage_string">This product is %d%% off.</string>
+</resources>

test/twine_test.rb

@@ -44,6 +44,14 @@ class TwineTest < Test::Unit::TestCase
     end
   end
 
+  def test_generate_string_file_6
+    Dir.mktmpdir do |dir|
+      output_path = File.join(dir, 'en.xml')
+      Twine::Runner.run(%W(generate-string-file test/fixtures/strings-3.txt #{output_path}))
+      assert_equal(ERB.new(File.read('test/fixtures/test-output-8.txt')).result, File.read(output_path))
+    end
+  end
+
   def test_consume_string_file_1
     Dir.mktmpdir do |dir|
       output_path = File.join(dir, 'strings.txt')