diff --git a/lib/markdown-it/deflist.js b/lib/markdown-it/deflist.js
index 8040ec39..7762af3b 100644
--- a/lib/markdown-it/deflist.js
+++ b/lib/markdown-it/deflist.js
@@ -1,5 +1,5 @@
 /**
- * Definition list
+ * Render a definition list
  *
  * @param {Function} md - markdown-it instance
  * @returns {Function} - markdown-it rendering rules
diff --git a/lib/markdown-it/footnote.js b/lib/markdown-it/footnote.js
index ba3525ed..e0c50e19 100644
--- a/lib/markdown-it/footnote.js
+++ b/lib/markdown-it/footnote.js
@@ -1,5 +1,5 @@
 /**
- * Footnotes
+ * Render footnotes
  *
  * @param {Function} md - markdown-it instance
  * @returns {Function} - markdown-it rendering rules
diff --git a/lib/markdown-it/table-of-contents.js b/lib/markdown-it/table-of-contents.js
index 816d93dd..bea30a6a 100644
--- a/lib/markdown-it/table-of-contents.js
+++ b/lib/markdown-it/table-of-contents.js
@@ -1,5 +1,5 @@
 /**
- * Table of contents
+ * Render a table of contents
  *
  * @param {Function} md - markdown-it instance
  * @returns {Function} - markdown-it rendering rules
diff --git a/lib/markdown-it/table.js b/lib/markdown-it/table.js
index 3ce0fe82..f80ba5b4 100644
--- a/lib/markdown-it/table.js
+++ b/lib/markdown-it/table.js
@@ -1,7 +1,5 @@
 /**
- * Responsive tables
- *
- * Add `tabindex` so that table scrolling can be controlled via the keyboard.
+ * Render a table with `tabindex` to enable keyboard scrolling
  *
  * @param {Function} md - markdown-it instance
  * @returns {Function} - markdown-it rendering rules
diff --git a/test/lib/markdown-it.mjs b/test/lib/markdown-it.mjs
new file mode 100644
index 00000000..35346887
--- /dev/null
+++ b/test/lib/markdown-it.mjs
@@ -0,0 +1,56 @@
+import { strict as assert } from 'node:assert'
+import { describe, it } from 'node:test'
+import md from '../../lib/markdown-it.js'
+
+describe('markdown-it', () => {
+  it('Returns configured markdown-it parser', () => {
+    const { options } = md()
+
+    assert.equal(options.breaks, true)
+    assert.equal(typeof options.highlight, 'function')
+    assert.equal(options.html, true)
+    assert.equal(options.linkify, false)
+    assert.equal(options.typographer, true)
+  })
+
+  it('Renders anchor heading permalinks when option enabled', () => {
+    const result = md({
+      headingPermalinks: true
+    }).render('# Heading')
+
+    assert.equal(result, '<h1 id="heading" tabindex="-1" class="govuk-heading-xl"><a class="app-link--heading govuk-link" href="#heading"><span>Heading</span></a></h1>\n')
+  })
+
+  it('Renders a definition list', () => {
+    const result = md().render('Term\n: Definition')
+
+    assert.match(result, /<dl class="app-definition-list"/)
+  })
+
+  it('Renders footnotes', () => {
+    const result = md().render('A[^1]\nB[^1]\n\n[^1]: One')
+
+    assert.match(result, /<sup id="fnref:1"/)
+    assert.match(result, /href="#fn:1"/)
+    assert.match(result, /<li id="fn:1"/)
+    assert.match(result, /href="#fnref:1"/)
+
+    assert.match(result, /<sup id="fnref:1:1"/)
+    assert.match(result, /href="#fn:1:1"/)
+  })
+
+  it('Renders a table of contents', () => {
+    const result = md().render('[[toc]]\n\n# A\n\n## B')
+
+    assert.match(result, /<nav class="app-contents-list"/)
+    assert.match(result, /aria-label="Contents"/)
+    assert.match(result, /href="#b"/)
+    assert.doesNotMatch(result, /href="#a"/)
+  })
+
+  it('Renders a table with `tabindex` to enable keyboard scrolling', () => {
+    const result = md().render('|A|B|\n|-|-|\n|1|2|')
+
+    assert.match(result, /<table tabindex="0"/)
+  })
+})