test: yield to warnings printer

Author: legendecas

test/fixtures/stacktrace.ts

@@ -1,4 +1,8 @@
 enum Foo {
 	A = "Hello, TypeScript!",
 }
-throw new Error(Foo.A);
+
+// Allow warnings about source maps to be shown for testing purposes.
+setImmediate(() => {
+  throw new Error(Foo.A);
+});