add tests

client/landing/stepper/hooks/test/use-start-url.tsx

@@ -0,0 +1,41 @@
+/**
+ * @jest-environment jsdom
+ */
+import { renderHook } from '@testing-library/react';
+import { useStartUrl } from '../use-start-url';
+
+jest.mock( 'calypso/boot/locale', () => ( {
+	getLocaleFromQueryParam: jest.fn().mockReturnValue( 'fr' ),
+	getLocaleFromPathname: jest.fn().mockReturnValue( 'fr' ),
+} ) );
+
+jest.mock( '../../utils/path', () => ( {
+	getLoginUrl: jest.fn().mockReturnValue( 'https://example.com/login' ),
+} ) );
+
+describe( 'useStartUrl', () => {
+	beforeAll( () => {
+		Object.defineProperty( window, 'location', {
+			value: {
+				search: '?aff=123&vid=456',
+				replace: jest.fn(), // Ensure this is mocked if used in your code
+				href: '',
+			},
+			writable: true, // Allow this definition to be writable if needed later
+		} );
+	} );
+
+	it( 'should generate the correct start URL', () => {
+		// Use the hook and assert results
+		const { result } = renderHook( () => useStartUrl( 'test-flow' ) );
+
+		expect( result.current ).toBe(
+			'https://example.com/login&redirect_to=/setup/test-flow%3Flocale%3Dfr&vid=456&aff=123'
+		);
+	} );
+
+	afterAll( () => {
+		// Restore the original window.location object after all tests are done
+		jest.restoreAllMocks();
+	} );
+} );