Do not panic if user puts strange things in tests directory

[mkaput]

Problem

Scarb tests directory target collector is building tests packages named from non-relevant files, like Scarb.toml. This results in trials to create packages named like foo_Scarb etc.

Steps

For the following project with the following tests directory:

https://github.com/gizatechxyz/orion/tree/bbf9833c437b83c7b4dd1fd4dde194717321628a/tests

After being run in Scarb 2.3.0, Scarb started panicking with:

thread 'main' panicked at scarb/src/core/package/name.rs:38:29:
called `Result::unwrap()` on an `Err` value: invalid package name: `orion_Scarb`
note: usage of ASCII uppercase letters in the package name has been disallowed
help: change package name to: orion_scarb
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Possible Solution(s)

Add an error condition in the test collector checking if there are unexpected files and bail with a user-friendly error message, which will cleanly describe what the user's project setup is doing wrong and how the user can fix it.

Notes

Starting point:

scarb/scarb/src/core/manifest/toml_manifest.rs

Line 581 in 5745ace

fn collect_test_targets(

Additional reference: https://discordapp.com/channels/793094838509764618/1166735890291372063/1166868590797013094

Version

2.3.0