svelte/test/runtime/samples/props-reactive-only-with-change/_config.js

let callbacks = [];

export default {
	props: {
		callback: (value) => callbacks.push(value),
		val1: '1',
		val2: '2'
	},

	before_test() {
		callbacks = [];
	},

	async test({ assert, component, target }) {
		assert.equal(callbacks.length, 2);
		assert.equal(JSON.stringify(callbacks), '["1","2"]');

		component.val1 = '3';
		assert.equal(callbacks.length, 3);
		assert.equal(JSON.stringify(callbacks), '["1","2","1"]');

		component.val1 = '4';
		assert.equal(callbacks.length, 4);
		assert.equal(JSON.stringify(callbacks), '["1","2","1","1"]');

		component.val2 = '5';
		assert.equal(callbacks.length, 5);
		assert.equal(JSON.stringify(callbacks), '["1","2","1","1","2"]');
	}
};