Add unit tests to test-cli

[MCarlomagno]

Description

In order to improve the quality of test-cli pkg, it would be good to add some unit tests for:

• cmd/test-cli/beacon.go
• cmd/test-cli/engine.go
• cmd/test-cli/requests.go
• cmd/test-cli/validator.go

Unfortunately, for most of those scripts it is required to refactor the code in order to inject dependencies, adding mocks and improving testability

[metachris]

test-cli is not actively maintained. are you using it?