test: improve ssz tests consistency

[jeluard]

Motivation

Make sure all tests always run

Description

Do not throw an error when an SSZ type is missing, but rather fail a test.
This let subsequent generated tests run not matter what, ensuring the tests count is consistent.

[nflaig]

doesn't this just result in strange errors downstream if we don't throw here and exit the test run?

[jeluard]

Makes sense. I updated so that when sszType is null, associated tests are not run at all; also improved the error message to be more meaningfull.
Compared to the original Error based approach, a missing SSZ type will not prevent further tests to be run (the Error would short-circuit the logic)

[nflaig]

Still not sure this improves the situation, could you provide the output of running the ssz_static tests with a missing ssz type before vs. after your changes

[jeluard]

The main thing that it improves, besides better error message giving some context, is that further tests are not short-circuited.
Currently all tests related to types defined after the missing one will not be generated/Executed as the Error short-circuit the whole dynamic test generation.
With this change, a single test fail related to the missing types, and all tests are run for further types (if they are existing).

[nflaig]

besides better error message giving some context, is that further tests are not short-circuited

I understand that but can you provide a before vs. after example

[wemeetagain]

Makes sense to me.
The test count is still variable, but at least one missing ssz type won't cause an unknown number of unrelated ssz type tests from being suppressed.