diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index a1861cb..6df6eb9 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -41,10 +41,9 @@ jobs:
                   composer-options: ${{ matrix.composer_flags }}
 
             - name: Install Composer dependencies (tests)
-              uses: ramsey/composer-install@v3
-              with:
-                  composer-options: ${{ matrix.composer_flags }}
-                  working-directory: tests/issue-13
+              run: php tests/install-deps.php
+              env:
+                  COMPOSER_FLAGS: ${{ matrix.composer_flags }}
 
             - run: vendor/bin/phpunit
               if: ${{ matrix.php_version != '8.2' }}
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 23900bf..4715d42 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -9,7 +9,8 @@
       <directory suffix="Test.php">tests/unit/</directory>
     </testsuite>
     <testsuite name="Functional tests">
-      <directory suffix=".phpt">tests/functional/</directory>
+      <directory suffix=".phpt">tests/functional/error-handler/</directory>
+      <file>tests/functional/nested-composer-projects/test.phpt</file>
       <file>tests/issue-13/test.phpt</file>
       <file>tests/issue-13/test-path-callback.phpt</file>
     </testsuite>
diff --git a/tests/functional/lists-all-classes-in-project.phpt b/tests/functional/lists-all-classes-in-project.phpt
index e98decb..4b671f8 100644
--- a/tests/functional/lists-all-classes-in-project.phpt
+++ b/tests/functional/lists-all-classes-in-project.phpt
@@ -5,9 +5,9 @@ ComposerFinder - should list all classes in a project w/o autoloading
 require __DIR__ . '/../../vendor/autoload.php';
 
 $finder = (new Kcs\ClassFinder\Finder\ComposerFinder())->useAutoloading(false);
-$classes = iterator_to_array($finder);
+iterator_to_array($finder);
 
-printf('> found %d class(es)' . PHP_EOL, count($classes));
+echo "OK";
 ?>
---EXPECTF--
-> found %d class(es)
+--EXPECT--
+OK
diff --git a/tests/functional/nested-composer-projects/composer.json b/tests/functional/nested-composer-projects/composer.json
new file mode 100644
index 0000000..47d7dad
--- /dev/null
+++ b/tests/functional/nested-composer-projects/composer.json
@@ -0,0 +1,11 @@
+{
+    "repositories": [
+        {
+            "type": "vcs",
+            "url": "../../.."
+        }
+    ],
+    "require": {
+        "kcs/class-finder": "^1.0@dev"
+    }
+}
diff --git a/tests/functional/nested-composer-projects/otherProject/composer.json b/tests/functional/nested-composer-projects/otherProject/composer.json
new file mode 100644
index 0000000..c1aa096
--- /dev/null
+++ b/tests/functional/nested-composer-projects/otherProject/composer.json
@@ -0,0 +1,5 @@
+{
+    "require": {
+        "nikic/php-parser": "^4.18 || ^5.0"
+    }
+}
diff --git a/tests/functional/nested-composer-projects/test.phpt b/tests/functional/nested-composer-projects/test.phpt
new file mode 100644
index 0000000..910cb6b
--- /dev/null
+++ b/tests/functional/nested-composer-projects/test.phpt
@@ -0,0 +1,14 @@
+--TEST--
+ComposerFinder - nested composer projects
+--FILE--
+<?php
+require_once 'vendor/autoload.php';
+$otherProjectClassLoader = require __DIR__ . '/otherProject/vendor/autoload.php';
+
+$finder = new Kcs\ClassFinder\Finder\ComposerFinder($otherProjectClassLoader);
+iterator_to_array($finder);
+
+echo "OK";
+?>
+--EXPECT--
+OK
diff --git a/tests/install-deps.php b/tests/install-deps.php
new file mode 100644
index 0000000..dc6fa52
--- /dev/null
+++ b/tests/install-deps.php
@@ -0,0 +1,39 @@
+<?php
+
+declare(strict_types=1);
+
+foreach (glob(__DIR__ . '/*') as $path) {
+    if (is_dir($path)) {
+        $files = new RecursiveIteratorIterator(
+            new RecursiveCallbackFilterIterator(
+                new RecursiveDirectoryIterator($path, FilesystemIterator::SKIP_DOTS | FilesystemIterator::FOLLOW_SYMLINKS),
+                static fn (SplFileInfo $file): bool => $file->getBasename()[0] !== '.',
+            ),
+            RecursiveIteratorIterator::LEAVES_ONLY | RecursiveIteratorIterator::CHILD_FIRST,
+        );
+
+        foreach ($files as $filepath => $info) {
+            if (! $info->isFile()) {
+                continue;
+            }
+
+            if ($info->getFilename() === 'composer.json') {
+                if (basename(dirname($info->getPath())) === 'vendor') {
+                    continue;
+                }
+
+                $descriptorspec = [STDIN, STDOUT, STDERR];
+                $proc = proc_open(trim('composer install ' . getenv('COMPOSER_FLAGS') ?: ''), $descriptorspec, $pipes, $info->getPath());
+                for ($running = true; $running;) {
+                    $status = proc_get_status($proc);
+                    $running = $status['running'];
+                    $exitcode = $status['exitcode'];
+                }
+
+                if ($exitcode !== 0) {
+                    return;
+                }
+            }
+        }
+    }
+}
diff --git a/tests/issue-13/test-path-callback.phpt b/tests/issue-13/test-path-callback.phpt
index 84dfecd..5ad9d8a 100644
--- a/tests/issue-13/test-path-callback.phpt
+++ b/tests/issue-13/test-path-callback.phpt
@@ -11,7 +11,8 @@ $count = 0;
 foreach ($finder as $className => $reflector) {
     ++$count;
 }
-printf('> found %d class(es)' . PHP_EOL, $count);
+
+echo "OK"
 ?>
---EXPECTF--
-> found %d class(es)
+--EXPECT--
+OK
diff --git a/tests/issue-13/test.phpt b/tests/issue-13/test.phpt
index c140e62..4a0f0d8 100644
--- a/tests/issue-13/test.phpt
+++ b/tests/issue-13/test.phpt
@@ -11,7 +11,8 @@ $count = 0;
 foreach ($finder as $className => $reflector) {
     ++$count;
 }
-printf('> found %d class(es)' . PHP_EOL, $count);
+
+echo "OK"
 ?>
---EXPECTF--
-> found %d class(es)
+--EXPECT--
+OK