unit tests now passing 

```
–(~/dart/discovery_api_dart_client_generator)–($ dart tool/hop_runner.dart test
test: generate - no args -- PASS
test: generate - help -- PASS
test: Library discovery_v1_api_client generated successfully.
test: generate - generate library via API and analyze -- PASS
test: generate - generate library via CLI -- PASS
test: generate - "rest" args should throw -- PASS
test: generate - missing output directory should throw -- PASS
test: 6 PASSED, 0 FAILED, 0 ERRORS
```