diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/closed-shadow-dom/_config.js b/packages/svelte/tests/runtime-browser/custom-elements-samples/closed-shadow-dom/_config.js
new file mode 100644
index 0000000000..9e09967dab
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/closed-shadow-dom/_config.js
@@ -0,0 +1,13 @@
+import { test } from '../../assert';
+const tick = () => Promise.resolve();
+
+export default test({
+	async test({ assert, target }) {
+		target.innerHTML = '<custom-element></custom-element>';
+		await tick();
+
+		const el = target.querySelector('custom-element');
+
+		assert.equal(el.shadowRoot, null);
+	}
+});
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/closed-shadow-dom/main.svelte b/packages/svelte/tests/runtime-browser/custom-elements-samples/closed-shadow-dom/main.svelte
new file mode 100644
index 0000000000..93744481b3
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/closed-shadow-dom/main.svelte
@@ -0,0 +1,3 @@
+<svelte:options customElement={{ tag: "custom-element", shadow: { mode: 'closed' } }} />
+
+<h1>Hello world!</h1>
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/shadow-root-init-options/_config.js b/packages/svelte/tests/runtime-browser/custom-elements-samples/shadow-root-init-options/_config.js
new file mode 100644
index 0000000000..106d27929e
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/shadow-root-init-options/_config.js
@@ -0,0 +1,18 @@
+import { test } from '../../assert';
+const tick = () => Promise.resolve();
+
+export default test({
+	async test({ assert, target }) {
+		target.innerHTML = '<custom-element></custom-element>';
+		await tick();
+
+		/** @type {ShadowRoot} */
+		const shadowRoot = target.querySelector('custom-element').shadowRoot;
+
+		assert.equal(shadowRoot.mode, 'open');
+		assert.equal(shadowRoot.clonable, true);
+		assert.equal(shadowRoot.delegatesFocus, true);
+		assert.equal(shadowRoot.serializable, true);
+		assert.equal(shadowRoot.slotAssignment, 'manual');
+	}
+});
diff --git a/packages/svelte/tests/runtime-browser/custom-elements-samples/shadow-root-init-options/main.svelte b/packages/svelte/tests/runtime-browser/custom-elements-samples/shadow-root-init-options/main.svelte
new file mode 100644
index 0000000000..25d69d7ef9
--- /dev/null
+++ b/packages/svelte/tests/runtime-browser/custom-elements-samples/shadow-root-init-options/main.svelte
@@ -0,0 +1,14 @@
+<svelte:options
+	customElement={{
+		tag: 'custom-element',
+		shadow: {
+			mode: 'open',
+			clonable: true,
+			delegatesFocus: true,
+			serializable: true,
+			slotAssignment: 'manual',
+		},
+	}}
+/>
+
+<h1>Hello world!</h1>