Fix issue with markdown lexer code fences

Fixes the bug reported in #1389, where the markdown lexer will not issue a
token for the closing code fence.

Issue: #1389

2 files changed, 34 insertions, 4 deletions

diff --git a/pygments/lexers/markup.py b/pygments/lexers/markup.py
index 92dc9e7a..e6265f40 100644
--- a/pygments/lexers/markup.py
+++ b/pygments/lexers/markup.py
@@ -536,10 +536,9 @@ class MarkdownLexer(RegexLexer):
         # no lexer for this language. handle it like it was a code block
         if lexer is None:
             yield match.start(4), String, code
-            return
-
-        for item in do_insertions([], lexer.get_tokens_unprocessed(code)):
-            yield item
+        else:
+            for item in do_insertions([], lexer.get_tokens_unprocessed(code)):
+                yield item
 
         yield match.start(5), String        , match.group(5)
 
diff --git a/tests/test_markdown_lexer.py b/tests/test_markdown_lexer.py
new file mode 100644
index 00000000..16d1f28d
--- /dev/null
+++ b/tests/test_markdown_lexer.py
@@ -0,0 +1,31 @@
+# -*- coding: utf-8 -*-
+"""
+    Pygments regex lexer tests
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+    :copyright: Copyright 2006-2017 by the Pygments team, see AUTHORS.
+    :license: BSD, see LICENSE for details.
+"""
+import unittest
+
+from pygments.lexers.markup import MarkdownLexer
+
+
+class SameTextTests(unittest.TestCase):
+
+    lexer = MarkdownLexer()
+
+    def assert_same_text(self, text):
+        """Show that lexed markdown does not remove any content. """
+        tokens = list(self.lexer.get_tokens_unprocessed(text))
+        output = ''.join(t[2] for t in tokens)
+        self.assertEqual(text, output)
+
+    def test_code_fence(self):
+        self.assert_same_text(r'```\nfoo\n```\n')
+
+    def test_code_fence_gsm(self):
+        self.assert_same_text(r'```markdown\nfoo\n```\n')
+
+    def test_code_fence_gsm_with_no_lexer(self):
+        self.assert_same_text(r'```invalid-lexer\nfoo\n```\n')