Restore test coverage in `cdf`

[vlopes11]

Is your feature request related to a problem? Please describe.
The commit dccf809 regressed the coverage since it reimplemented most of the library.

Describe the solution you'd like
We need to test the library again, preferably with fuzzing techniques, or fuzzy-friendly frameworks.

For reference:

• quickcheck
• cargo-fuzz
• msgpacker fuzz

Describe alternatives you've considered
We can implement normal unit tests, but the branching coverage of these is usually harder to improve

Additional context
N/A