add test for programmatic prefetch

test/app/routes/about.html

@@ -7,12 +7,13 @@
 
 	<p>This is the 'about' page. There's not much here.</p>
 
-	<button on:click='goto("/blog/what-is-sapper")'>What is Sapper?</button>
+	<button class='goto' on:click='goto("/blog/what-is-sapper")'>What is Sapper?</button>
+	<button class='prefetch' on:click='goto("/blog/why-the-name")'>Why the name?</button>
 </Layout>
 
 <script>
 	import Layout from './_components/Layout.html';
-	import { goto } from '../../../runtime.js';
+	import { goto, prefetch } from '../../../runtime.js';
 
 	export default {
 		components: {
@@ -20,7 +21,8 @@
 		},
 
 		methods: {
-			goto
+			goto,
+			prefetch
 		}
 	};
 </script>

test/common/test.js

@@ -166,7 +166,7 @@ function run(env) {
 			});
 
 			it('navigates to a new page without reloading', async () => {
-				await nightmare.goto(base).wait(() => window.READY).wait(100);
+				await nightmare.goto(base).wait(() => window.READY).wait(200);
 
 				const requests = await capture(async () => {
 					await nightmare.click('a[href="/about"]');
@@ -189,7 +189,7 @@ function run(env) {
 				await nightmare
 					.goto(`${base}/about`)
 					.wait(() => window.READY)
-					.click('button')
+					.click('.goto')
 					.wait(() => window.location.pathname === '/blog/what-is-sapper')
 					.wait(100);
 
@@ -199,6 +199,20 @@ function run(env) {
 				);
 			});
 
+			it('prefetches programmatically', async () => {
+				await nightmare
+					.goto(`${base}/about`)
+					.wait(() => window.READY);
+
+				const requests = await capture(async () => {
+					return await nightmare
+						.click('.prefetch')
+						.wait(100);
+				});
+
+				assert.ok(!!requests.find(r => r.url === '/api/blog/why-the-name'));
+			});
+
 			it('scrolls to active deeplink', async () => {
 				const scrollY = await nightmare
 					.goto(`${base}/blog/a-very-long-post#four`)