add test

test/runtime/samples/component-not-constructor/Sub.svelte

@@ -0,0 +1 @@
+<div>Sub</div>

test/runtime/samples/component-not-constructor/_config.js

@@ -0,0 +1,11 @@
+export default {
+	skip_if_ssr: true,
+	skip_if_hydrate_from_ssr: true,
+	compileOptions: {
+		dev: true
+	},
+	props: {
+		selected: false
+	},
+	error: 'this={...} of <svelte:component> should specify a Svelte component.'
+};

test/runtime/samples/component-not-constructor/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Sub from './Sub.svelte';
+	export let selected;
+	let banana = {};
+	let component = banana;
+	$: selected ? component = Sub : component = banana;
+</script>
+
+<svelte:component this={component} />

test/runtime/samples/component-not-constructor2/Sub.svelte

@@ -0,0 +1 @@
+<div>Sub</div>

test/runtime/samples/component-not-constructor2/_config.js

@@ -0,0 +1,16 @@
+export default {
+	compileOptions: {
+		dev: true
+	},
+	props: {
+		selected: true
+	},
+	test({ assert, component }) {
+		try {
+			component.selected = false;
+			throw new Error('Expected an error');
+		} catch (err) {
+			assert.equal(err.message, 'this={...} of <svelte:component> should specify a Svelte component.');
+		}
+	}
+};

test/runtime/samples/component-not-constructor2/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Sub from './Sub.svelte';
+	export let selected;
+	let banana = {};
+	let component = banana;
+	$: selected ? component = Sub : component = banana;
+</script>
+
+<svelte:component this={component} />