test behaviour of objects

packages/svelte/tests/runtime-runes/samples/state-link-object/_config.js

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+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<button>0</button><button>0</button><button>0</button>`,
+
+	test({ assert, target }) {
+		const [btn1, btn2, btn3] = target.querySelectorAll('button');
+
+		flushSync(() => btn1.click());
+		assert.htmlEqual(target.innerHTML, `<button>1</button><button>1</button><button>1</button>`);
+
+		// mutate the original object, via the link
+		flushSync(() => btn2.click());
+		assert.htmlEqual(target.innerHTML, `<button>2</button><button>2</button><button>2</button>`);
+
+		// mutate the copy
+		flushSync(() => btn3.click());
+		assert.htmlEqual(target.innerHTML, `<button>2</button><button>2</button><button>3</button>`);
+
+		flushSync(() => btn1.click());
+		assert.htmlEqual(target.innerHTML, `<button>3</button><button>3</button><button>3</button>`);
+	}
+});

packages/svelte/tests/runtime-runes/samples/state-link-object/main.svelte

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+<script>
+	let a = $state({ value: 0 });
+	let b = $state.link(a);
+	let c = $state.link({ ...a });
+</script>
+
+<button onclick={() => a.value++}>{a.value}</button>
+<button onclick={() => b.value++}>{b.value}</button>
+<button onclick={() => c.value++}>{c.value}</button>