🧪 [testing improvement] add unit tests for GitHub API header generation

- Added `tests/test_api.js` to verify header generation in `src/api.js`.
- Included test cases for `githubHeaders` and `apiHeaders`.
- Followed the project's existing testing pattern using Node.js `vm` module.

Co-authored-by: TauNeutrino <1600410+TauNeutrino@users.noreply.github.com>

tests/test_api.js

@@ -0,0 +1,72 @@
+const fs = require('fs');
+const vm = require('vm');
+const path = require('path');
+
+console.log("=== Running API Unit Tests ===");
+
+// 1. Load Source Code
+const apiPath = path.join(__dirname, '..', 'src', 'api.js');
+const constantsPath = path.join(__dirname, '..', 'src', 'constants.js');
+
+let apiCode = fs.readFileSync(apiPath, 'utf8');
+let constantsCode = fs.readFileSync(constantsPath, 'utf8');
+
+// Strip exports and imports for VM
+apiCode = apiCode.replace(/export /g, '').replace(/import .*? from .*?;/g, '');
+constantsCode = constantsCode.replace(/export /g, '');
+
+// 2. Setup Mock Environment
+const sandbox = {
+    console: console,
+};
+
+try {
+    vm.createContext(sandbox);
+    // Load constants first as api.js might depend on them
+    vm.runInContext(constantsCode, sandbox);
+    vm.runInContext(apiCode, sandbox);
+
+    console.log("--- Testing githubHeaders ---");
+    const ghHeaders = sandbox.githubHeaders();
+    console.log("Result:", JSON.stringify(ghHeaders));
+
+    if (ghHeaders['Accept'] !== 'application/vnd.github.v3+json') {
+        throw new Error(`Expected Accept header 'application/vnd.github.v3+json', but got '${ghHeaders['Accept']}'`);
+    }
+    console.log("✅ githubHeaders Test Passed");
+
+    console.log("--- Testing apiHeaders ---");
+
+    // Test with token
+    const token = 'test-token';
+    const headersWithToken = sandbox.apiHeaders(token);
+    console.log("With token:", JSON.stringify(headersWithToken));
+    if (headersWithToken['Authorization'] !== `Token ${token}`) {
+        throw new Error(`Expected Authorization header 'Token ${token}', but got '${headersWithToken['Authorization']}'`);
+    }
+
+    // Test without token (should use GUEST_TOKEN)
+    const headersWithoutToken = sandbox.apiHeaders();
+    console.log("Without token:", JSON.stringify(headersWithoutToken));
+    const guestToken = vm.runInContext('GUEST_TOKEN', sandbox);
+    if (headersWithoutToken['Authorization'] !== `Token ${guestToken}`) {
+        throw new Error(`Expected Authorization header 'Token ${guestToken}', but got '${headersWithoutToken['Authorization']}'`);
+    }
+
+    if (headersWithoutToken['Accept'] !== 'application/json') {
+        throw new Error(`Expected Accept header 'application/json', but got '${headersWithoutToken['Accept']}'`);
+    }
+
+    const clientVersion = vm.runInContext('CLIENT_VERSION', sandbox);
+    if (headersWithoutToken['X-Client-Version'] !== clientVersion) {
+        throw new Error(`Expected X-Client-Version header '${clientVersion}', but got '${headersWithoutToken['X-Client-Version']}'`);
+    }
+
+    console.log("✅ apiHeaders Test Passed");
+
+    console.log("ALL API TESTS PASSED ✅");
+
+} catch (e) {
+    console.error("❌ API Unit Test Error:", e);
+    process.exit(1);
+}