kp: tests (#910)

| [![PR App][icn]][demo] | Fix RM-XYZ |
| :--------------------: | :--------: |

## 🧰 Changes

Describe your changes in detail.

## 🧬 QA & Testing

- [Broken on production][prod].
- [Working in this PR app][demo].

[demo]: https://markdown-pr-PR_NUMBER.herokuapp.com
[prod]: https://SUBDOMAIN.readme.io
[icn]:
https://user-images.githubusercontent.com/886627/160426047-1bee9488-305a-4145-bb2b-09d8b757d38a.svg

__tests__/compilers/html-block.test.ts

@@ -0,0 +1,33 @@
+import { mdast, mdx } from '../../index';
+
+describe('html-block compiler', () => {
+  it('compiles html blocks within containers', () => {
+    const markdown = `
+> 🚧 It compiles!
+>
+> <HTMLBlock>{\`
+>   <strong style="color: olive">Hello, World!</strong>
+> \`}</HTMLBlock>
+`;
+
+    expect(mdx(mdast(markdown)).trim()).toBe(markdown.trim());
+  });
+
+  it('compiles html blocks with indents', () => {
+    const markdown = `
+<HTMLBlock>{\`
+  <pre><code>
+const foo = () => {
+  const bar = {
+    baz: 'blammo'
+  }
+
+  return bar
+}
+  </code></pre>
+\`}</HTMLBlock>
+`;
+
+    expect(mdx(mdast(markdown)).trim()).toBe(markdown.trim());
+  });
+});