Escape characters in test failures

Unit tests results.xml are incorrectly generated. Escape special characters for junit report

Sample:
```

/usr/local/share/lua/5.1/mocka.lua:600: assertEquals failed: expected [allowed], was [{"error_code":"403013","message":"Your IP is not whitelisted"}
]

```

Locate the code that generates results.xml and inspect how failure messages from the sample are written into the JUnit report. Verify the expected escaping for special characters and confirm that the resulting XML is valid while preserving the failure message content.

Written by the indexing model from the issue text.