tests: add integration tests

[tshakalekholoane]

Is your feature request related to a problem? Please describe.

Improve coverage by adding integration tests. The cmd crate has test keys that can be used to achieve this.

Describe the solution you'd like

Perhaps using something like assert_cmd or clap's Command::debug_assert.

Describe alternatives you've considered

Writing unit tests that read a key and ensure that it is parsed correctly. This would probably be enough given the individual primitives already have tests in the relevant standards modules.