Split support in the Vercel Serverless adapter (#7514)

* start of vercel split support

* Split Mode with the Vercel Adapter

* Write routes into the config.json

* Add a changeset

* Add docs

* Better changeset

1 files changed, 29 insertions, 0 deletions

diff --git a/packages/integrations/vercel/test/split.test.js b/packages/integrations/vercel/test/split.test.js
new file mode 100644
index 000000000..b89a428be
--- /dev/null
+++ b/packages/integrations/vercel/test/split.test.js
@@ -0,0 +1,29 @@
+import { loadFixture } from './test-utils.js';
+import { expect } from 'chai';
+
+describe('build: split', () => {
+	/** @type {import('./test-utils').Fixture} */
+	let fixture;
+
+	before(async () => {
+		fixture = await loadFixture({
+			root: './fixtures/basic/',
+			output: 'server',
+			build: {
+				split: true,
+			}
+		});
+		await fixture.build();
+	});
+
+	it('creates separate functions for each page', async () => {
+		const files = await fixture.readdir('../.vercel/output/functions/')
+		expect(files.length).to.equal(2);
+	});
+
+	it('creates the route definitions in the config.json', async () => {
+		const json = await fixture.readFile('../.vercel/output/config.json');
+		const config = JSON.parse(json);
+		expect(config.routes).to.have.a.lengthOf(3);
+	})
+});