Don't mutate the text node while pretty printing

lib/rexml/formatters/pretty.rb

@@ -86,9 +86,8 @@ def write_element(node, output)
       end
 
       def write_text( node, output )
-        s = node.to_s()
-        s.gsub!(/\s/,' ')
-        s.squeeze!(" ")
+        # Not gsub!/squeeze!: Text#to_s returns the node's own string.
+        s = node.to_s().gsub(/\s/, ' ').squeeze(" ")
         s = wrap(s, @width - @level)
         s = indent_text(s, @level, " ", true)
         output << (' '*@level + s)

test/formatter/test_pretty.rb

@@ -0,0 +1,34 @@
+module REXMLTests
+  class PrettyFormatterTest < Test::Unit::TestCase
+    def format(node, indentation=2)
+      formatter = REXML::Formatters::Pretty.new(indentation)
+      output = +""
+      formatter.write(node, output)
+      output
+    end
+
+    class TextTest < self
+      def test_source_document_is_not_modified
+        document = REXML::Document.new("<a><b>hello   world</b></a>")
+        format(document)
+        assert_equal("<a><b>hello   world</b></a>", document.to_s)
+      end
+
+      def test_raw_text_value_is_not_modified
+        text = REXML::Text.new("hello   world", true, nil, true)
+        format(text)
+        assert_equal("hello   world", text.value)
+      end
+
+      def test_whitespace_is_replaced_with_space
+        document = REXML::Document.new("<a><b>x\ty</b></a>")
+        assert_equal("<a>\n  <b>\n    x y\n  </b>\n</a>", format(document))
+      end
+
+      def test_consecutive_spaces_are_squeezed
+        document = REXML::Document.new("<a><b>x   y</b></a>")
+        assert_equal("<a>\n  <b>\n    x y\n  </b>\n</a>", format(document))
+      end
+    end
+  end
+end