Add tests for Updater input validation

[ivanayov]

This test covers targetinfo, target_path, target_base_url,
metadata_dir and filepath input validation of the Updater
methods

Fixes #1644

• The code follows the Code Style Guidelines
• Tests have been added for the bug fix or new feature
• [n/a] Docs have been added for the bug fix or new feature

[coveralls]

Pull Request Test Coverage Report for Build 1778436409

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

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Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.9%) to 98.609%

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Totals
Change from base Build 1777896864:	0.9%
Covered Lines:	3943
Relevant Lines:	3970

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💛 - Coveralls

[MVrachev]

What I like as a result of this pr is that we can see what exceptions are thrown by different Updater public API functions.
I am planning on fixing the TODO items related to Raises documentation in the public function docstrings from tuf/ngclient/updater.py.

[jku]

good find, another non-documented Securesystemslib error.. we can handle this in a separate issue though

[jku]

#1761

[jku]

I've left some specific comments in source.

A general comment on testing any download failures or Fetcher errors: They seem like good new ideas but it might be more useful to add those into test_updater_ng.py as testing this aspect with Repositorysimulator is going to be quite artificial: there's not even a webserver involved...

I think that applies to second half of test_empty_targetinfo_validation and test_invalid_target_base_url.

[ivanayov]

Linter is failing for examples/repo_example/hashed_bin_delegation.py which is not related to the current changes. I addressed the requirements to verify locally that tox will pass, but didn't commit the change, as it's not related to the PR. This probably came with some linter update, as the file was not changed recently. Can address this in a separate PR.

[MVrachev]

@ivanayov you can rebase your pr on develop.
The pr #1814 which fixes the linting problem was merged.

[ivanayov]

@MVrachev thank you for addressing the issue! I just pushed an update.

[jku]

I think two of the tests do not give us much value and could be removed.

Other tests look good... Although we're left with just two short local storage tests in the new file: maybe it's not worth it to add 50 lines of setup code for two tests? We could just move those two to test_updater_ng.py?

[jku]

Approving, these look good.

I left this question that wasn't responded to though:

...we're left with just two short local storage tests in the new file: maybe it's not worth it to add 50 lines of setup code for two tests? We could just move those two to test_updater_ng.py?

no need to do it now, just wondering about that