diff --git a/frontend/src/lib/person/relationship/AddRelationshipForm.svelte.test.ts b/frontend/src/lib/person/relationship/AddRelationshipForm.svelte.test.ts
index 4ad56a54..705fee7b 100644
--- a/frontend/src/lib/person/relationship/AddRelationshipForm.svelte.test.ts
+++ b/frontend/src/lib/person/relationship/AddRelationshipForm.svelte.test.ts
@@ -88,4 +88,77 @@ describe('AddRelationshipForm', () => {
 		// but at least verify the prop is wired (no crash).
 		expect(onSubmit).not.toHaveBeenCalled();
 	});
+
+	it('renders with use:enhance form action when onSubmit is undefined', async () => {
+		render(AddRelationshipForm, { props: { personId: 'p-1' } });
+
+		await page.getByRole('button', { name: /hinzufügen/i }).click();
+		await new Promise((r) => setTimeout(r, 30));
+
+		const form = document.querySelector('form[action="?/addRelationship"]');
+		expect(form).not.toBeNull();
+	});
+
+	it('renders the callback-based form when onSubmit is provided', async () => {
+		render(AddRelationshipForm, { props: { personId: 'p-1', onSubmit: async () => {} } });
+
+		await page.getByRole('button', { name: /hinzufügen/i }).click();
+		await new Promise((r) => setTimeout(r, 30));
+
+		// callback form has no action attribute (just onsubmit handler)
+		const enhancedForm = document.querySelector('form[action="?/addRelationship"]');
+		expect(enhancedForm).toBeNull();
+		const fallbackForm = document.querySelector('form');
+		expect(fallbackForm).not.toBeNull();
+	});
+
+	it('shows the self-error when the related person id equals personId', async () => {
+		render(AddRelationshipForm, { props: { personId: 'p-self' } });
+
+		await page.getByRole('button', { name: /hinzufügen/i }).click();
+		await new Promise((r) => setTimeout(r, 30));
+
+		// Set the relatedPersonId hidden input to match personId
+		const relInput = document.querySelector('input[name="relatedPersonId"]') as HTMLInputElement;
+		relInput.value = 'p-self';
+		relInput.dispatchEvent(new Event('input', { bubbles: true }));
+		await new Promise((r) => setTimeout(r, 30));
+
+		await expect.element(page.getByText(/selbst|self/i)).toBeVisible();
+	});
+
+	it('keeps submit disabled when no related person is selected', async () => {
+		render(AddRelationshipForm, { props: { personId: 'p-1' } });
+
+		await page.getByRole('button', { name: /hinzufügen/i }).click();
+		await new Promise((r) => setTimeout(r, 30));
+
+		// The "Hinzufügen" button changed from toggle button → submit button. Find the submit one.
+		const submitBtn = Array.from(
+			document.querySelectorAll('button[type="submit"]')
+		)[0] as HTMLButtonElement;
+		expect(submitBtn.disabled).toBe(true);
+	});
+
+	it('keeps submit disabled when there is a yearError', async () => {
+		render(AddRelationshipForm, { props: { personId: 'p-1' } });
+
+		await page.getByRole('button', { name: /hinzufügen/i }).click();
+
+		const fromInput = document.querySelector('input[name="fromYear"]') as HTMLInputElement;
+		const toInput = document.querySelector('input[name="toYear"]') as HTMLInputElement;
+		const relInput = document.querySelector('input[name="relatedPersonId"]') as HTMLInputElement;
+		fromInput.value = '1923';
+		fromInput.dispatchEvent(new Event('input', { bubbles: true }));
+		toInput.value = '1920';
+		toInput.dispatchEvent(new Event('input', { bubbles: true }));
+		relInput.value = 'p-other';
+		relInput.dispatchEvent(new Event('input', { bubbles: true }));
+
+		await new Promise((r) => setTimeout(r, 30));
+		const submitBtn = Array.from(
+			document.querySelectorAll('button[type="submit"]')
+		)[0] as HTMLButtonElement;
+		expect(submitBtn.disabled).toBe(true);
+	});
 });