Add (failing) test case for multiple mapper errors with stop on error

- Add a failing test case to indicate that only 1 of the mapper errors is catchable when stop on error is true and many mappers throw an exception
- With concurrent mappers it seems that exceptions should throw an AggregateError when stop on error is true and more than 1 concurrent mapper throws - the iteration of new input items should stop immediately, but all invoked mappers need to finish and all of their exceptions should be bundled and rejected at once - maybe?

test.js

@@ -225,3 +225,36 @@ test('catches exception from source iterator - 2nd item after 1st item mapper th
 	t.is(input.index, 2);
 	t.deepEqual(mappedValues, [0]);
 });
+
+test('no unhandled rejected promises from mapper throws - infinite concurrency', async t => {
+	const input = [1, 2, 3];
+	const mappedValues = [];
+	await t.throwsAsync(
+		pMap(input, async value => {
+			mappedValues.push(value);
+			await delay(100);
+			throw new Error(`Oops! ${value}`);
+		}),
+		{message: 'Some big AggregateError message'}
+	);
+	// Note: all 3 mappers get invoked, all 3 throw, even with stop on error this
+	// should raise an AggregateError with all 3 exceptions instead of throwing 1
+	// exception and hiding the other 2.
+	t.deepEqual(mappedValues, [1, 2, 3]);
+});
+
+test('no unhandled rejected promises from mapper throws - concurrency 1', async t => {
+	const input = [1, 2, 3];
+	const mappedValues = [];
+	await t.throwsAsync(
+		pMap(input, async value => {
+			mappedValues.push(value);
+			await delay(100);
+			throw new Error(`Oops! ${value}`);
+		},
+		{concurrency: 1}),
+		{message: 'Oops! 1'}
+	);
+	t.deepEqual(mappedValues, [1]);
+});
+