anchor.diff:        var expected = '<element xmlns:foo="http://1.foo.com/" />';
         expect(actual, expected);
       });
  -    test('unused namespace optimized', () {
  +    test('unused namespace (optimized)', () {
         var builder = new XmlBuilder(optimizeNamespaces: true);
         builder.element('element', nest: () {
           builder.namespace('http://1.foo.com/', 'foo');
  
positive.code:       var expected = '<foo:element xmlns:foo="http://1.foo.com/" />';
        expect(actual, expected);
      });
      test('conflicting namespace optimized', () {
        var builder = new XmlBuilder(optimizeNamespaces: true);
        builder.element('element', nest: () {
          builder.namespace('http://1.foo.com/', 'foo');
          expect(() => builder.namespace('http://2.foo.com/', 'foo'),
              throwsArgumentError);
        }, namespace: 'http://1.foo.com/');
        var actual = builder.build().toString();
        var expected = '<foo:element xmlns:foo="http://1.foo.com/" />';
        expect(actual, expected);
      });
      test('unused namespace', () {
        var builder = new XmlBuilder(optimizeNamespaces: false);
        builder.element('element', nest: () {
          builder.namespace('http://1.foo.com/', 'foo');
        });
  
negative.code:       var expected = '<element />';
        expect(actual, expected);
      });
      test('conflicting namespace', () {
        var builder = new XmlBuilder();
        builder.element('element', nest: () {
          builder.namespace('http://1.foo.com/', 'foo');
          expect(() => builder.namespace('http://2.foo.com/', 'foo'),
  