tools/doc: Add tests for the toHTML function

Addresses nodejs#5955 on GitHub.
Test the toHTML function in html.js. Check that given valid markdown it
produces the expected html. One test case will prevent regressions of
big nodejs#5873.

tools/doc/tests/fixtures/order_of_end_tags_5873.markdown

@@ -0,0 +1,6 @@
+# Title
+
+## Subsection
+
+### Class Method: Buffer.from(array)
+* `array` {Array}

tools/doc/tests/fixtures/sample_document.markdown

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+# Sample Markdown
+
+## Seussian Rhymes
+1. fish
+2. fish
+
+* Red fish
+* Blue fish

tools/doc/tests/test_html.js

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+'use strict';
+
+var assert = require('assert');
+var fs = require('fs');
+
+var html = require('../html.js');
+
+// Outputs valid html when given simple markdown
+function test_toHTML() {
+  // Test data is a list of objects with two properties.
+  // The file property is the file path.
+  // The html property is some html which will be generated by the doctool.
+  // This html will be stripped of all whitespace.
+  var testData = [
+    {
+      'file': 'tools/doc/tests/fixtures/sample_document.markdown',
+      'html': '<ol><li>fish</li><li><p>fish</p></li><li><p>Redfish</p></li>' +
+        '<li>Bluefish</li></ol>'
+    },
+    {
+      'file': 'tools/doc/tests/fixtures/order_of_end_tags_5873.markdown',
+      'html': '<h3>ClassMethod: Buffer.from(array) <span> ' +
+        '<a class="mark" href="#foo_class_method_buffer_from_array" ' +
+        'id="foo_class_method_buffer_from_array">#</a> </span> </h3><div' +
+        'class="signature"><ul><li><code>array</code><a ' +
+        'href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/' +
+        'Reference/Global_Objects/Array" class="type">&lt;Array&gt;</a></li>' +
+        '</ul></div>'
+    },
+  ];
+
+  testData.forEach(function(item) {
+    // Normalize expected data by stripping whitespace
+    var expected = item.html.replace(/\s/g, '');
+
+    fs.readFile(item.file, 'utf8', function(err, input) {
+      html(input, 'foo', 'doc/template.html', function(err, output) {
+
+        if (err) throw err;
+
+        var actual = output.replace(/\s/g, '');
+        // Assert that the input stripped of all whitespace contains the
+        // expected list
+        assert.notEqual(actual.indexOf(expected), -1);
+      });
+    });
+  });
+}
+
+test_toHTML();