Dev Task: Improve test coverage of wps_shared package

[dgboss]

Describe the task
When wps_shared was separated out we lost a lot of code coverage. Test in the api and wps_jobs packages exercise code paths in wps_shared but this 'doesn't count' in terms of code coverage when running wps_shared tests. We've had to lower the code cov target to 70%.

Acceptance Criteria

• Write tests to get wps_shared code cov to > 80%
• Increase the target threshold in code_cov.yml back to 80%.

Additional context

• Add any other context about the task here.
• Or here