chore(widget-markdown): add failing commonmark spec (#2263)

packages/netlify-cms-widget-markdown/src/serializers/__tests__/commonmark.spec.js

@@ -0,0 +1,30 @@
+import { flow, trim } from 'lodash';
+import commonmarkSpec from './__fixtures__/commonmark.json';
+import { markdownToSlate, slateToMarkdown, markdownToHtml } from '../index.js';
+
+/**
+ * Map the commonmark spec data into an array of arrays for use in Jest's
+ * `test.each`.
+ */
+const spec = commonmarkSpec.map(({ markdown, html }) => [markdown, html]);
+
+/**
+ * Each test receives input markdown and output html as expected for Commonmark
+ * compliance. To test all of our handling in one go, we serialize the markdown
+ * into our Slate AST, then back to raw markdown, and finally to HTML.
+ */
+const process = flow([markdownToSlate, slateToMarkdown, markdownToHtml]);
+
+/**
+ * Passing this test suite requires 100% Commonmark compliance. There are 624
+ * tests, of which we're passing about 300 as of introduction of this suite. To
+ * work on improving Commonmark support, remove `.skip` from this `describe`
+ * and run the test suite locally.
+ */
+describe.skip('Commonmark support', () => {
+  test.each(spec)('%s', (markdown, html) => {
+    // We're trimming the html from the spec as they all have trailing newlines
+    // and we never output trailing newlines. This may be a compliance issue.
+    expect(process(markdown)).toEqual(trim(html));
+  });
+});