These async methods are a replacement for the Observable based `runSchematicAsync` and `runExternalSchematicAsync` methods.
DEPRECATED:
The Observable based `SchematicTestRunner.runSchematicAsync` and `SchematicTestRunner.runExternalSchematicAsync` method have been deprecated in favor of the Promise based `SchematicTestRunner.runSchematic` and `SchematicTestRunner.runExternalSchematic`.