fix: provide explicit test paths and filter for PHPUnit in CI

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
       run: composer install --prefer-dist --no-progress
 
     - name: Run test suite
-      run: vendor/bin/phpunit --coverage-text
+      run: vendor/bin/phpunit --coverage-text --coverage-filter src tests/Unit tests/Integration
 
     - name: Run Static Analysis (PHPStan)
       run: vendor/bin/phpstan analyse src --level 5

phpunit.xml

@@ -0,0 +1,20 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/10.5/phpunit.xsd"
+         bootstrap="vendor/autoload.php"
+         colors="true"
+         cacheDirectory=".phpunit.cache">
+    <testsuites>
+        <testsuite name="Unit">
+            <directory>tests/Unit</directory>
+        </testsuite>
+        <testsuite name="Integration">
+            <directory>tests/Integration</directory>
+        </testsuite>
+    </testsuites>
+    <source>
+        <include>
+            <directory>src</directory>
+        </include>
+    </source>
+</phpunit>