added unit test for checkbox markdown syntax

tests/lib/markdown-test.js

@@ -20,3 +20,8 @@ test('Markdown.render() should renders KaTeX correctly', t => {
   const rendered = md.render(markdownFixtures.katex)
   t.snapshot(rendered)
 })
+
+test('Markdown.render() should renders checkboxes', t => {
+  const rendered = md.render(markdownFixtures.checkboxes)
+  t.snapshot(rendered)
+})

tests/lib/snapshots/markdown-test.js.md

@@ -51,4 +51,14 @@ Generated by [AVA](https://ava.li).
     <li><a href="http://bit.ly/2z8BUJZ">Twitter</a></li>␊
     <li><a href="http://bit.ly/2jcca8t">Facebook Group</a></li>␊
     </ul>␊
-    `
+    
+
+## Markdown.render() should renders checkboxes
+
+> Snapshot 1
+
+    `<ul>␊
+    <li class="taskListItem"><input type="checkbox" id="checkbox-2" /> Unchecked</li>␊
+    <li class="taskListItem"><input type="checkbox" checked id="checkbox-3" /> Checked</li>␊
+    </ul>␊
+    `