test: improve coverage for ref/ref.mbt

[rami3l]

Disclaimer: This PR was generated by an LLM agent as part of an experiment.

Summary

coverage of `ref/ref.mbt`: 71.4% -> 85.7%

[peter-jerry-ye-code-review]

‼️ This code review is generated by a bot. Please verify the content before trusting it.

Looking at the git diff, I don't see any immediate critical problems, but here are a couple of observations and suggestions:

1. The new test case uses inspect! macro with content parameter to check the string representation, but using assert_eq! with direct value comparison might be more reliable and conventional for testing, similar to how it's done in the test case above it.

2. When testing with strings, it's generally good practice to also test with strings containing special characters or empty strings to ensure proper handling. The current test only uses a simple "hello" string.

These are relatively minor points, and the code appears generally sound. The diff shows the addition of a new test case for string reference creation, which seems to be a valid and reasonable addition to the test suite.

[coveralls]

Pull Request Test Coverage Report for Build 5026

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.02%) to 85.024%

---

Totals
Change from base Build 5019:	0.02%
Covered Lines:	5223
Relevant Lines:	6143

---

💛 - Coveralls