diff --git a/packages/kit/src/runtime/server/parse_body/read_only_form_data.spec.js b/packages/kit/src/runtime/server/parse_body/read_only_form_data.spec.js
new file mode 100644
index 000000000000..a792e00967b4
--- /dev/null
+++ b/packages/kit/src/runtime/server/parse_body/read_only_form_data.spec.js
@@ -0,0 +1,59 @@
+import { test } from 'uvu';
+import * as assert from 'uvu/assert';
+import { read_only_form_data } from './read_only_form_data.js';
+
+const { data, append } = read_only_form_data();
+append('foo', '1'), append('foo', '2'), append('foo', '3');
+append('bar', '2'), append('bar', '1');
+
+test('ro-fd get returns first value', () => {
+	assert.equal(data.get('foo'), '1');
+	assert.equal(data.get('bar'), '2');
+});
+
+test('ro-fd getAll returns array', () => {
+	assert.equal(data.getAll('foo'), ['1', '2', '3']);
+	assert.equal(data.getAll('bar'), ['2', '1']);
+});
+
+test('ro-fd has returns boolean flag', () => {
+	assert.equal(data.has('foo'), true);
+	assert.equal(data.has('bar'), true);
+	assert.equal(data.has('baz'), false);
+});
+
+test('ro-fd iterator yields all key-value pairs', () => {
+	const values = [];
+	for (const [key, val] of data) values.push({ key, val });
+
+	assert.equal(values.length, 5);
+	assert.equal(values[0], { key: 'foo', val: '1' });
+	assert.equal(values[3], { key: 'bar', val: '2' });
+});
+
+test('ro-fd entries() yields all key-value pairs', () => {
+	const values = [];
+	for (const [key, val] of data.entries()) values.push({ key, val });
+
+	assert.equal(values.length, 5);
+	assert.equal(values[0], { key: 'foo', val: '1' });
+	assert.equal(values[3], { key: 'bar', val: '2' });
+});
+
+test('ro-fd keys() yields all unique keys', () => {
+	const values = [];
+	for (const key of data.keys()) values.push(key);
+
+	assert.equal(values.length, 2);
+	assert.equal(values, ['foo', 'bar']);
+});
+
+test('ro-fd values() yields all nested values', () => {
+	const values = [];
+	for (const val of data.values()) values.push(val);
+
+	assert.equal(values.length, 5);
+	assert.equal(values, ['1', '2', '3', '2', '1']);
+});
+
+test.run();