diff --git a/tests/Providers/Rng/CSRNGProviderTest.php b/tests/Providers/Rng/CSRNGProviderTest.php
index 39739e9..abb6488 100644
--- a/tests/Providers/Rng/CSRNGProviderTest.php
+++ b/tests/Providers/Rng/CSRNGProviderTest.php
@@ -11,11 +11,18 @@ class CSRNGProviderTest extends TestCase
 {
     use NeedsRngLengths;
 
+    /**
+     * @requires function random_bytes
+     */
     public function testCSRNGProvidersReturnExpectedNumberOfBytes(): void
     {
-        $rng = new CSRNGProvider();
-        foreach ($this->rngTestLengths as $l) {
-            $this->assertSame($l, strlen($rng->getRandomBytes($l)));
+        if (function_exists('random_bytes')) {
+            $rng = new CSRNGProvider();
+            foreach ($this->rngTestLengths as $l) {
+                $this->assertSame($l, strlen($rng->getRandomBytes($l)));
+            }
+        } else {
+            $this->expectNotToPerformAssertions();
         }
     }
 }
diff --git a/tests/Providers/Rng/IRNGProviderTest.php b/tests/Providers/Rng/IRNGProviderTest.php
index fd2c742..743774a 100644
--- a/tests/Providers/Rng/IRNGProviderTest.php
+++ b/tests/Providers/Rng/IRNGProviderTest.php
@@ -15,4 +15,17 @@ class IRNGProviderTest extends TestCase
         $tfa = new TwoFactorAuth('Test', 6, 30, Algorithm::Sha1, null, null);
         $this->assertIsString($tfa->createSecret());
     }
+
+    public function testCreateSecretGeneratesDesiredAmountOfEntropy(): void
+    {
+        $rng = new TestRNGProvider();
+
+        $tfa = new TwoFactorAuth('Test', 6, 30, Algorithm::Sha1, null, $rng);
+        $this->assertSame('A', $tfa->createSecret(5));
+        $this->assertSame('AB', $tfa->createSecret(6));
+        $this->assertSame('ABCDEFGHIJKLMNOPQRSTUVWXYZ', $tfa->createSecret(128));
+        $this->assertSame('ABCDEFGHIJKLMNOPQRSTUVWXYZ234567', $tfa->createSecret(160));
+        $this->assertSame('ABCDEFGHIJKLMNOPQRSTUVWXYZ234567ABCDEFGHIJKLMNOPQRSTUVWXYZ234567', $tfa->createSecret(320));
+        $this->assertSame('ABCDEFGHIJKLMNOPQRSTUVWXYZ234567ABCDEFGHIJKLMNOPQRSTUVWXYZ234567A', $tfa->createSecret(321));
+    }
 }
diff --git a/tests/Providers/Rng/TestRNGProvider.php b/tests/Providers/Rng/TestRNGProvider.php
new file mode 100644
index 0000000..fd5b591
--- /dev/null
+++ b/tests/Providers/Rng/TestRNGProvider.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Providers\Rng;
+
+use RobThree\Auth\Providers\Rng\IRNGProvider;
+
+class TestRNGProvider implements IRNGProvider
+{
+    /**
+     * {@inheritdoc}
+     */
+    public function getRandomBytes(int $bytecount): string
+    {
+        $result = '';
+
+        for ($i = 0; $i < $bytecount; $i++) {
+            $result .= chr($i);
+        }
+
+        return $result;
+    }
+}