@@ -0,0 +1,44 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+
+import { u } from 'unist-builder';
+
+import transformDiagrams, { renderDiagram } from '../diagrams.mjs';
+
+const transform = transformDiagrams();
+
+describe('transformDiagrams', () => {
+  it('renders ```dot code blocks as inline SVG', () => {
+    const tree = u('root', [u('code', { lang: 'dot' }, 'digraph { a -> b }')]);
+
+    transform(tree);
+
+    const [node] = tree.children;
+    assert.equal(node.type, 'html');
+    assert.match(
+      node.value,
+      /^<div class="diagram">[\s\S]*<svg[\s\S]*<\/svg><\/div>$/
+    );
+    assert.doesNotMatch(node.value, /\n\s*\n/);
+  });
+
+  it('leaves other code blocks alone', () => {
+    const code = u('code', { lang: 'js' }, 'a -> b');
+    const tree = u('root', [code]);
+
+    transform(tree);
+
+    assert.equal(tree.children[0], code);
+  });
+});
+
+describe('renderDiagram', () => {
+  it('renders a diagram per color scheme for themed colors', () => {
+    const html = renderDiagram('digraph { a [color="${#000000|#ffffff}"] }');
+
+    assert.match(html, /class="diagram diagram-light"/);
+    assert.match(html, /class="diagram diagram-dark"/);
+    assert.match(html.split('diagram-dark')[0], /#000000/);
+    assert.match(html.split('diagram-dark')[1], /#ffffff/);
+  });
+});