BREAKING CHANGE
Deprecated `SchematicTestRunner.runSchematic` and `SchematicTestRunner.runExternalSchematic` have been removed. Use `SchematicTestRunner.runSchematicAsync` or `SchematicTestRunner.runExternalSchematicAsync` instead.
Note: this change only effects direct `@angular-devkit/schematics` users and not the application developers.
All schematics can potentially be async. The synchronous test method variants (`runSchematic`/`runExternalSchematic`) will fail if the schematic, any of its rules, or any schematic it calls are async.