Allow running tests without a bundle

[vinistock]

Motivation

Closes #3561

It's not uncommon for Rubyists to have unit tests for some scripts that do not have any dependencies (no bundle). There were two issues preventing us from running tests:

1. Because there's no bundle, we never index the parent class (e.g.: Minitest::Test) and so the linearized ancestors the class only end up including itself
2. We were using an incorrect Bundler helper to determine the base command

Implementation

For 1, I started checking if there's only the class itself in the list of ancestors, which indicates that we're hitting this scenario. In that case, I started including the parent class if available, which allows us to discover tests.

Note that there's one limitation: if the user introduces an intermediate parent class, we won't be able to discover the tests.

For 2, the method we should've been using is with_unbundled_env, which removes Bundler related variables and allows us to discover if there's a main bundle in the project.

Automated Tests

Added a test that reproduces.

[vinistock]

• Allow running tests without a bundle #3689 👈 (View in Graphite)
• main

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