test: add a bunch of tests from bluebird

Take tests from Bluebird's promisify's tests and adapted them to the
format in use here.
Add tests making sure things work with async functions.
Add basic usability tests.

PR-URL: #12442
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: William Kapke <william.kapke@gmail.com>
Reviewed-By: Timothy Gu <timothygu99@gmail.com>
Reviewed-By: Teddy Katz <teddy.katz@gmail.com>

test/parallel/test-util-promisify.js

@@ -74,3 +74,97 @@ const stat = promisify(fs.stat);
     assert.strictEqual(value, undefined);
   }));
 }
+
+{
+  function fn(err, val, callback) {
+    callback(err, val);
+  }
+  promisify(fn)(null, 42).then(common.mustCall((value) => {
+    assert.strictEqual(value, 42);
+  }));
+}
+
+{
+  function fn(err, val, callback) {
+    callback(err, val);
+  }
+  promisify(fn)(new Error('oops'), null).catch(common.mustCall((err) => {
+    assert.strictEqual(err.message, 'oops');
+  }));
+}
+
+{
+  function fn(err, val, callback) {
+    callback(err, val);
+  }
+
+  (async () => {
+    const value = await promisify(fn)(null, 42);
+    assert.strictEqual(value, 42);
+  })();
+}
+
+{
+  const o = {};
+  const fn = promisify(function(cb) {
+
+    cb(null, this === o);
+  });
+
+  o.fn = fn;
+
+  o.fn().then(common.mustCall(function(val) {
+    assert(val);
+  }));
+}
+
+{
+  const err = new Error('Should not have called the callback with the error.');
+  const stack = err.stack;
+
+  const fn = promisify(function(cb) {
+    cb(null);
+    cb(err);
+  });
+
+  (async () => {
+    await fn();
+    await Promise.resolve();
+    return assert.strictEqual(stack, err.stack);
+  })();
+}
+
+{
+  function c() { }
+  const a = promisify(function() { });
+  const b = promisify(a);
+  assert.notStrictEqual(c, a);
+  assert.strictEqual(a, b);
+}
+
+{
+  let errToThrow;
+  const thrower = promisify(function(a, b, c, cb) {
+    errToThrow = new Error();
+    throw errToThrow;
+  });
+  thrower(1, 2, 3)
+    .then(assert.fail)
+    .then(assert.fail, (e) => assert.strictEqual(e, errToThrow));
+}
+
+{
+  const err = new Error();
+
+  const a = promisify((cb) => cb(err))();
+  const b = promisify(() => { throw err; })();
+
+  Promise.all([
+    a.then(assert.fail, function(e) {
+      assert.strictEqual(err, e);
+    }),
+    b.then(assert.fail, function(e) {
+      assert.strictEqual(err, e);
+    })
+  ]);
+}