fix: testing-isolation do not force run all if no packages were found

[davidcavazos]

Description

Currently, if all diff files are in the ignore list, it's considered as a global change. This is not necessary since a non-ignored file will return the "." package, which will correctly trigger all tests. If no packages were found that's because files should be ignored and no tests should be run. Added a test case to cover this.

Checklist

• I have followed guidelines from CONTRIBUTING.MD and Samples Style Guide
• Tests pass: npm test (see Testing)
• Lint pass: npm run lint (see Style)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This pull request is from a branch created directly off of GoogleCloudPlatform/nodejs-docs-samples. Not a fork.
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new sample directory, and I created GitHub Actions workflow for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[code-review-assist]

Hi team,

I'm currently reviewing this pull request and will have a full review ready in a few minutes. In the meantime, here's a quick summary to get everyone up to speed:

This pull request addresses an issue where the testing isolation mechanism incorrectly forced the execution of all tests even when no packages were found. The core change is to prevent this behavior. The intent is to improve the efficiency of the testing process by avoiding unnecessary test runs when no relevant changes are detected.

Here's a breakdown of the changes:

• File Changed: .github/cloud-samples-tools/pkg/config/config.go
• Change Summary: Removed the logic that returned "." (all packages) when no changed packages were found. This prevents unnecessary test runs when all changes are ignored. Lines 180-182 were removed.

The updated logic ensures that if no packages are identified as changed, no tests are run, leading to a more efficient and targeted testing process.

---

And now, a little haiku to lighten the mood:

Tests run swift and true,
No need for all, just the changed,
Efficiency reigns.

Thanks,
Gemini

[code-review-assist]

This pull request fixes an issue where a global change was triggered even when all diff files were ignored. The fix correctly identifies that if no packages are found, it's because the files should be ignored, and therefore no tests should run. This change improves the accuracy of the test runner and prevents unnecessary test executions. The added test case is a good addition and covers the new behavior. I've summarized the style guide elements I referenced below.

Referenced Style Guide Elements:

• General: Encouraged adding comments to explain the logic behind returning an empty slice. While the code is relatively straightforward, a brief comment can enhance understanding, especially for new contributors.
• Go Style Guide: Comments should be clear and concise, explaining the why behind the code, not just the what.