svelte/test/runtime/samples/binding-select-null-placeholder/_config.js

const items = [ { id: 'a' }, { id: 'b' } ];

export default {
	props: {
		foo: null,
		items
	},

	test({ assert, component, target }) {
		const select = target.querySelector( 'select' );
		const options = target.querySelectorAll( 'option' );

		assert.equal( options[0].selected, true );
		assert.equal( options[0].disabled, true );
		assert.equal( options[1].selected, false );
		assert.equal( options[1].disabled, false );

		// placeholder option value must be blank string for native required field validation
		assert.equal( options[0].value, '' );
		assert.equal( select.checkValidity(), false );

		component.foo = items[0];

		assert.equal( options[0].selected, false );
		assert.equal( options[1].selected, true );
		assert.equal( select.checkValidity(), true );
	}
};