svelte/test/runtime/samples/observe-prevents-loop/_config.js

export default {
	props: {
		thing: { a: 1 }
	},

	test(assert, component) {
		const thing = component.thing;

		component.on('state', ({ changed, current }) => {
			if (changed.thing) {
				const { thing } = current;
				thing.b = thing.a * 2;
				component.thing = thing; // triggers infinite loop, unless event handler breaks it
			}
		});

		assert.deepEqual(thing, {
			a: 1
		});

		thing.a = 3;
		component.thing = thing;

		assert.deepEqual(thing, {
			a: 3,
			b: 6
		});
	}
};