Start the test suite

For starters, let's just verify that the webhook validation manages to
dismiss requests that have the wrong method.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

__tests__/index.test.js

@@ -0,0 +1,27 @@
+const index = require('../GitForWindowsHelper/index')
+
+process.env['GITHUB_WEBHOOK_SECRET'] = 'for-testing'
+
+test('reject requests other than webhook payloads', async () => {
+    const context = {
+        log: jest.fn(),
+        req: {
+            method: 'GET'
+        }
+    }
+
+    const expectInvalidWebhook = async (message) => {
+        context.log.mockClear()
+        expect(await index(context, context.req)).toBeUndefined()
+        expect(context.log).toHaveBeenCalledTimes(1)
+        // context.log was called with an instance of an `Error`
+        expect(context.log.mock.calls[0][0].message).toEqual(message)
+        expect(context.res).toEqual({
+            body: `Go away, you are not a valid GitHub webhook: Error: ${message}`,
+            headers: undefined,
+            status: 403
+        })
+    }
+
+    await expectInvalidWebhook('Unexpected method: GET')
+})