tools: add tests for the doctool

* Test the toHTML function in html.js. Check that given valid markdown
  it produces the expected html. One test case will prevent regressions
  of #5873.
* Check that when given valid markdown toJSON produces valid JSON with
  the expected schema.
* Add doctool to the list of built in tests so it runs in CI.

PR-URL: https://github.com/nodejs/node/pull/6031
Fixes: https://github.com/nodejs/node/issues/5955
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: Rich Trott <rtrott@gmail.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/test/fixtures/order_of_end_tags_5873.md b/test/fixtures/order_of_end_tags_5873.md
new file mode 100644
index 0000000000..3eb7dadcb3
--- /dev/null
+++ b/test/fixtures/order_of_end_tags_5873.md
@@ -0,0 +1,6 @@
+# Title
+
+## Subsection
+
+### Class Method: Buffer.from(array)
+* `array` {Array}