Add fenced code block tests

pkgs/markdown/test/markdown_test.dart

diff --git a/pkgs/markdown/test/markdown_test.dart b/pkgs/markdown/test/markdown_test.dart
index 3875de0..fcf76d1 100644
--- a/pkgs/markdown/test/markdown_test.dart
+++ b/pkgs/markdown/test/markdown_test.dart
@@ -5,12 +5,11 @@
 /// Unit tests for markdown.
 library markdownTests;
 
+import 'package:unittest/unittest.dart';
+
 // TODO(rnystrom): Use "package:" URL (#4968).
 import '../lib/markdown.dart';
 
-// TODO(rnystrom): Better path to unittest.
-import 'package:unittest/unittest.dart';
-
 /// Most of these tests are based on observing how showdown behaves:
 /// http://softwaremaniacs.org/playground/showdown-highlight/
 void main() {
@@ -425,6 +424,35 @@
         ''');
   });
 
+  group('Fenced code blocks', () {
+    validate('without an optional language identifier', '''
+        ```
+        code
+        ```
+        ''', '''
+        <pre><code>code
+        </code></pre>
+        ''');
+
+    validate('with an optional language identifier', '''
+        ```dart
+        code
+        ```
+        ''', '''
+        <pre><code>code
+        </code></pre>
+        ''');
+
+    validate('escape HTML characters', '''
+        ```
+        <&>
+        ```
+        ''', '''
+        <pre><code>&lt;&amp;&gt;
+        </code></pre>
+        ''');
+  });
+
   group('Horizontal rules', () {
     validate('from dashes', '''
         ---
@@ -649,6 +677,12 @@
         second</code> after</p>
         ''');
 
+    validate('simple double backticks', '''
+        before ``source`` after
+        ''', '''
+        <p>before <code>source</code> after</p>
+        ''');
+
     validate('double backticks', '''
         before ``can `contain` backticks`` after
         ''', '''
@@ -798,6 +832,29 @@
         <p>links <a href="http://foo.com"><em>are</em></a> awesome</p>
         ''');
   });
+
+  group('Resolver', () {
+    var nyanResolver = (text) => new Text('~=[,,_${text}_,,]:3');
+    validate('simple resolver', '''
+        resolve [this] thing
+        ''', '''
+        <p>resolve ~=[,,_this_,,]:3 thing</p>
+        ''', linkResolver: nyanResolver);
+  });
+
+  group('Custom inline syntax', () {
+    List<InlineSyntax> nyanSyntax =
+      [new TextSyntax('nyan', sub: '~=[,,_,,]:3')];
+    validate('simple inline syntax', '''
+        nyan
+        ''', '''
+        <p>~=[,,_,,]:3</p>
+        ''', inlineSyntaxes: nyanSyntax);
+
+    // TODO(amouravski): need more tests here for custom syntaxes, as some
+    // things are not quite working properly. The regexps are sometime a little
+    // too greedy, I think.
+  });
 }
 
 /**
@@ -825,16 +882,17 @@
     }
   }
 
-  return Strings.join(lines, '\n');
+  return lines.join('\n');
 }
 
 validate(String description, String markdown, String html,
-         {bool verbose: false}) {
+         {bool verbose: false, inlineSyntaxes, linkResolver}) {
   test(description, () {
     markdown = cleanUpLiteral(markdown);
     html = cleanUpLiteral(html);
 
-    var result = markdownToHtml(markdown);
+    var result = markdownToHtml(markdown, inlineSyntaxes: inlineSyntaxes,
+        linkResolver: linkResolver);
     var passed = compareOutput(html, result);
 
     if (!passed) {