added unit tests

phpunit.xml

@@ -0,0 +1,30 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd"
+         bootstrap="tests/bootstrap.php"
+         colors="true"
+         cacheDirectory=".phpunit.cache"
+         failOnRisky="true"
+         failOnWarning="true">
+    <testsuites>
+        <testsuite name="unit">
+            <directory>tests/Unit</directory>
+        </testsuite>
+        <testsuite name="integration">
+            <directory>tests/Integration</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <!-- common.php is legacy/shared helpers; coverage focuses on API surface (lib, handlers, db_init). -->
+        <include>
+            <directory suffix=".php">lib</directory>
+            <directory suffix=".php">handlers</directory>
+            <file>db_init.php</file>
+            <file>common.php</file>
+        </include>
+        <exclude>
+            <directory>tests</directory>
+            <directory>vendor</directory>
+        </exclude>
+    </source>
+</phpunit>