Unit and integration tests have been failing due to failed logging of
`Error` objects. These were creating an issue where `mocha` was not
properly returning right exit codes, leading to test pipelines
incorrectly passing despite test failures.
- Fix runtime behavior of failing to retrieve error stacks.
- Add tests for error handling.
- Add more robust custom error handling.
Related issues: babel/babel#14273, vuejs/vue-cli#6994.
