svelte/test/runtime/samples/transition-js-each-block-intro/_config.js

export default {
	data: {
		things: [ 'a', 'b', 'c' ]
	},

	test ( assert, component, target, window, raf ) {
		let divs = target.querySelectorAll( 'div' );
		assert.equal( divs[0].foo, 0 );
		assert.equal( divs[1].foo, 0 );
		assert.equal( divs[2].foo, 0 );

		raf.tick( 50 );
		assert.equal( divs[0].foo, 0.5 );
		assert.equal( divs[1].foo, 0.5 );
		assert.equal( divs[2].foo, 0.5 );

		component.set({ things: [ 'a', 'b', 'c', 'd' ] });
		divs = target.querySelectorAll( 'div' );
		assert.equal( divs[0].foo, 0.5 );
		assert.equal( divs[1].foo, 0.5 );
		assert.equal( divs[2].foo, 0.5 );
		assert.equal( divs[3].foo, 0 );

		raf.tick( 75 );
		assert.equal( divs[0].foo, 0.75 );
		assert.equal( divs[1].foo, 0.75 );
		assert.equal( divs[2].foo, 0.75 );
		assert.equal( divs[3].foo, 0.25 );

		component.destroy();
	}
};