Summary

Adds test/test_unit.cpp to cover critical gaps in test coverage. All 22 tests pass (5 existing + 17 new).

New tests

callback (8 tests)

• Null out and in pointers return 0
• size == 0 or num == 0 return 0
• size * num overflow returns 0
• Normal single and multi-chunk appends

Client construction & config (4 tests)

• Empty and populated parameter maps
• setTimeout() with positive and zero values

Edge cases / network (4 tests)

• Special characters (&, spaces) in location query — verifies URL encoding
• Empty query string — verifies no crash
• Default params at construction merged with per-call params
• search() always returns a parseable JSON object

Thread safety (1 test)

• 4 concurrent location() calls verify std::call_once CURL init is race-free

What still requires mocking to test

• curl_easy_init() returning null (OOM)
• curl_easy_perform() network failure path
• HasParseError() branch (needs injected bad response body)
• curl_easy_escape() null return (OOM)

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