test: add code cov to ut

[wenytang-ms]

https://app.codecov.io/github/microsoft/vscode-azureapicenter/commit/bd1badd62d3b3719ea7967b8468d11c68449c838

[codecov-commenter]

Welcome to Codecov :tada:

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

Thanks for integrating Codecov - We've got you covered :open_umbrella: