tests: show context.log() output upon failure

Since we mock away the `log()` function, the output is hidden from the
user. But in case of failures, that output is really valuable in
diagnosing issues! So let's intercept the exceptions and show the output
before re-throwing them.

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

Author: dscho

__tests__/index.test.js

@@ -82,8 +82,8 @@ const makeContext = (body, headers) => {
     }
 }
 
-const mockIssueComment = (comment) => {
-    return makeContext({
+const testIssueComment = (comment, fn) => {
+    const context = makeContext({
         action: 'created',
         comment: {
             body: comment,
@@ -108,10 +108,18 @@ const mockIssueComment = (comment) => {
     }, {
         'x-github-event': 'issue_comment'
     })
+
+    test(`test ${comment}`, async () => {
+        try {
+            await fn(context)
+        } catch (e) {
+            context.log.mock.calls.forEach(e => console.log(e[0]))
+            throw e;
+        }
+    })
 }
 
-test('test /hi', async () => {
-    const context = mockIssueComment('/hi')
+testIssueComment('/hi', async (context) => {
     expect(await index(context, context.req)).toBeUndefined()
     expect(context.res).toEqual({
         body: 'I said hi! new-comment-url-Hi @statler and waldorf!',