Basic test cases carrier billing payment

[PedroDiez]

What type of PR is this?

• tests

What this PR does / why we need it:

Basic Tests for Carrier Billing API

Which issue(s) this PR fixes:

Partially Fixes #159

Special notes for reviewers:

Tests for Carrier Billing Refund will be uploaded in a separate PR

Changelog input

 Basic tests for Carrier Billing API

Additional documentation

N/A

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ ACTION	actionlint	2		0	0.03s
✅ OPENAPI	spectral	2		0	3.94s
✅ REPOSITORY	git_diff	yes		no	0.05s
✅ REPOSITORY	secretlint	yes		no	1.04s
✅ YAML	yamllint	2		0	0.83s

See detailed report in MegaLinter reports

MegaLinter is graciously provided by

[bigludo7]

Thanks Pedro for the effort.
No major issue from my perspective but some small things that I have caught.

[bigludo7]

Thanks Pedro for the corrections.
I went thru and this is OK for me.

[PedroDiez]

Thanks for the review Ludovic!