Add test

test/runtime/samples/context-setcontext-return/_config.js

@@ -0,0 +1,5 @@
+export default {
+	html: `
+		<div>true</div>
+	`,
+};

test/runtime/samples/context-setcontext-return/main.svelte

@@ -0,0 +1,7 @@
+<script>
+    import { setContext } from 'svelte';
+    let a = {};
+    let b = setContext('foo', a);
+</script>
+
+<div>{a === b}</div>