Add some tests for mustache span syntax

Also refactored test files a bit

tests/markdown/basic.test.js

@@ -0,0 +1,15 @@
+/* eslint-disable max-lines */
+
+const Markdown = require('naturalcrit/markdown.js');
+
+test('Escapes <script> tag', function() {
+  const source = '<script></script>';
+  const rendered = Markdown.render(source);
+  expect(rendered).toMatch('&lt;script&gt;&lt;/script&gt;');
+});
+
+test('Processes the markdown within an HTML block if its just a class wrapper', function() {
+  const source = '<div>*Bold text*</div>';
+  const rendered = Markdown.render(source);
+  expect(rendered).toBe('<div> <p><em>Bold text</em></p>\n </div>');
+});