diff --git a/src/app/Utils.php b/src/app/Utils.php
--- a/src/app/Utils.php
+++ b/src/app/Utils.php
@@ -339,24 +339,6 @@
         return $asArray ? [$local, $domain] : "{$local}@{$domain}";
     }
 
-    /**
-     * Provide all unique combinations of elements in $input, with order and duplicates irrelevant.
-     *
-     * @param array $input The input array of elements.
-     *
-     * @return array[]
-     */
-    public static function powerSet(array $input): array
-    {
-        $output = [];
-
-        for ($x = 0; $x < count($input); $x++) {
-            self::combine($input, $x + 1, 0, [], 0, $output);
-        }
-
-        return $output;
-    }
-
     /**
      * Returns the current user's email address or null.
      *
@@ -435,30 +417,6 @@
         return (string) Str::uuid();
     }
 
-    private static function combine($input, $r, $index, $data, $i, &$output): void
-    {
-        $n = count($input);
-
-        // Current cobination is ready
-        if ($index == $r) {
-            $output[] = array_slice($data, 0, $r);
-            return;
-        }
-
-        // When no more elements are there to put in data[]
-        if ($i >= $n) {
-            return;
-        }
-
-        // current is included, put next at next location
-        $data[$index] = $input[$i];
-        self::combine($input, $r, $index + 1, $data, $i + 1, $output);
-
-        // current is excluded, replace it with next (Note that i+1
-        // is passed, but index is not changed)
-        self::combine($input, $r, $index, $data, $i + 1, $output);
-    }
-
     /**
      * Create self URL
      *
diff --git a/src/tests/Unit/DomainTest.php b/src/tests/Unit/DomainTest.php
--- a/src/tests/Unit/DomainTest.php
+++ b/src/tests/Unit/DomainTest.php
@@ -22,7 +22,7 @@
             Domain::STATUS_VERIFIED,
         ];
 
-        $domains = \App\Utils::powerSet($statuses);
+        $domains = \Tests\Utils::powerSet($statuses);
 
         foreach ($domains as $domainStatuses) {
             $domain = new Domain(
@@ -90,7 +90,7 @@
             Domain::TYPE_EXTERNAL,
         ];
 
-        $domains = \App\Utils::powerSet($types);
+        $domains = \Tests\Utils::powerSet($types);
 
         foreach ($domains as $domain_types) {
             $domain = new Domain(
diff --git a/src/tests/Unit/SharedFolderTest.php b/src/tests/Unit/SharedFolderTest.php
--- a/src/tests/Unit/SharedFolderTest.php
+++ b/src/tests/Unit/SharedFolderTest.php
@@ -20,7 +20,7 @@
             SharedFolder::STATUS_IMAP_READY,
         ];
 
-        $folders = \App\Utils::powerSet($statuses);
+        $folders = \Tests\Utils::powerSet($statuses);
 
         $folder = new SharedFolder(['name' => 'test']);
 
diff --git a/src/tests/Unit/UserTest.php b/src/tests/Unit/UserTest.php
--- a/src/tests/Unit/UserTest.php
+++ b/src/tests/Unit/UserTest.php
@@ -81,7 +81,7 @@
             User::STATUS_RESTRICTED,
         ];
 
-        $users = \App\Utils::powerSet($statuses);
+        $users = \Tests\Utils::powerSet($statuses);
 
         foreach ($users as $user_statuses) {
             $user = new User(
diff --git a/src/tests/Unit/UtilsTest.php b/src/tests/Unit/UtilsTest.php
--- a/src/tests/Unit/UtilsTest.php
+++ b/src/tests/Unit/UtilsTest.php
@@ -99,20 +99,20 @@
     }
 
     /**
-     * Test for Utils::powerSet()
+     * Test for Tests\Utils::powerSet()
      */
     public function testPowerSet(): void
     {
         $set = [];
 
-        $result = Utils::powerSet($set);
+        $result = \Tests\Utils::powerSet($set);
 
         $this->assertIsArray($result);
         $this->assertCount(0, $result);
 
         $set = ["a1"];
 
-        $result = Utils::powerSet($set);
+        $result = \Tests\Utils::powerSet($set);
 
         $this->assertIsArray($result);
         $this->assertCount(1, $result);
@@ -120,7 +120,7 @@
 
         $set = ["a1", "a2"];
 
-        $result = Utils::powerSet($set);
+        $result = \Tests\Utils::powerSet($set);
 
         $this->assertIsArray($result);
         $this->assertCount(3, $result);
@@ -130,7 +130,7 @@
 
         $set = ["a1", "a2", "a3"];
 
-        $result = Utils::powerSet($set);
+        $result = \Tests\Utils::powerSet($set);
 
         $this->assertIsArray($result);
         $this->assertCount(7, $result);
diff --git a/src/tests/Utils.php b/src/tests/Utils.php
new file mode 100644
--- /dev/null
+++ b/src/tests/Utils.php
@@ -0,0 +1,53 @@
+<?php
+
+namespace Tests;
+
+use Illuminate\Support\Str;
+
+/**
+ * Small utility functions for tests
+ */
+class Utils
+{
+    /**
+     * Provide all unique combinations of elements in $input, with order and duplicates irrelevant.
+     *
+     * @param array $input The input array of elements.
+     *
+     * @return array[]
+     */
+    public static function powerSet(array $input): array
+    {
+        $output = [];
+
+        for ($x = 0; $x < count($input); $x++) {
+            self::combine($input, $x + 1, 0, [], 0, $output);
+        }
+
+        return $output;
+    }
+
+    private static function combine($input, $r, $index, $data, $i, &$output): void
+    {
+        $n = count($input);
+
+        // Current cobination is ready
+        if ($index == $r) {
+            $output[] = array_slice($data, 0, $r);
+            return;
+        }
+
+        // When no more elements are there to put in data[]
+        if ($i >= $n) {
+            return;
+        }
+
+        // current is included, put next at next location
+        $data[$index] = $input[$i];
+        self::combine($input, $r, $index + 1, $data, $i + 1, $output);
+
+        // current is excluded, replace it with next (Note that i+1
+        // is passed, but index is not changed)
+        self::combine($input, $r, $index, $data, $i + 1, $output);
+    }
+}