diff --git a/.gitignore b/.gitignore
index 51b3172..9d9db20 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,5 +1,4 @@
 /vendor
 /.idea
 .DS_Store
-phpunit.xml
 composer.lock
diff --git a/composer.json b/composer.json
index 6ba772f..4896d86 100644
--- a/composer.json
+++ b/composer.json
@@ -1,5 +1,6 @@
 {
     "name": "codercat/jwk-to-pem",
+    "description": "Convert JWK to PEM format.",
     "type": "library",
     "license": "MIT",
     "authors": [
@@ -11,12 +12,22 @@
     "minimum-stability": "dev",
     "require": {
         "php": ">=7.0.0",
-        "phpseclib/phpseclib": "~2.0",
-        "ext-gmp": "*"
+        "phpseclib/phpseclib": "~2.0"
+    },
+    "require-dev": {
+        "phpunit/phpunit": "^7.0"
+    },
+    "suggest": {
+        "ext-gmp":""
     },
     "autoload": {
         "psr-4": {
             "CoderCat\\JWKToPEM\\": "src/"
         }
+    },
+    "autoload-dev": {
+        "psr-4": {
+            "CoderCat\\JWKToPEM\\Tests\\": "tests/"
+        }
     }
 }
diff --git a/phpunit.xml b/phpunit.xml
new file mode 100644
index 0000000..c9fe927
--- /dev/null
+++ b/phpunit.xml
@@ -0,0 +1,10 @@
+<phpunit
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/7.5/phpunit.xsd"
+         bootstrap="vendor/autoload.php">
+  <testsuites>
+    <testsuite name="unit tests">
+        <directory>tests</directory>
+    </testsuite>
+  </testsuites>
+</phpunit>
diff --git a/src/JWKConverter.php b/src/JWKConverter.php
index 9c4ff44..750831c 100644
--- a/src/JWKConverter.php
+++ b/src/JWKConverter.php
@@ -19,6 +19,14 @@
 class JWKConverter
 {
 
+    /** @var Base64UrlDecoder */
+    private $base64UrlDecoder;
+
+    public function __construct(?Base64UrlDecoder $base64UrlDecoder = null)
+    {
+        $this->base64UrlDecoder = $base64UrlDecoder ?? new Base64UrlDecoder();
+    }
+
     /**
      * @param array $jwk
      * @return string
@@ -40,11 +48,10 @@ public function toPEM(array $jwk): string
         }
 
         $rsa = new RSA();
-        $base64UrlDecoder = new Base64UrlDecoder();
         $rsa->loadKey(
             [
                 'e' => new BigInteger(base64_decode($jwk['e']), 256),
-                'n' => new BigInteger($base64UrlDecoder->decode($jwk['n']), 256)
+                'n' => new BigInteger($this->base64UrlDecoder->decode($jwk['n']), 256)
             ]
         );
         return $rsa->getPublicKey();
diff --git a/tests/JWKConverterTest.php b/tests/JWKConverterTest.php
new file mode 100644
index 0000000..d8b5c12
--- /dev/null
+++ b/tests/JWKConverterTest.php
@@ -0,0 +1,48 @@
+<?php
+namespace CoderCat\JWKToPEM\Tests;
+
+use CoderCat\JWKToPEM\JWKConverter;
+use PHPUnit\Framework\TestCase;
+
+class JWKConverterTest extends TestCase
+{
+    /** @var JWKConverter */
+    private $jwkConverter;
+
+    protected function setUp()
+    {
+        parent::setUp();
+        $this->jwkConverter = new JwkConverter();
+    }
+
+    /** @dataProvider provideToPem */
+    public function testToPem($jwk, $expected)
+    {
+        $this->assertEquals($expected, $this->jwkConverter->toPem($jwk));
+    }
+
+    public function provideToPem()
+    {
+        return [
+            [
+                [
+                    "kty" => "RSA",
+                    "kid" => "zhA-H1DWOSgWQAIW7mewCYeaZLGpkgW_hXfq8jmV99I",
+                    "use" => "sig",
+                    "alg" => "RS256",
+                    "e" => "AQAB",
+                    "n" => "vdv73smpkrTIBSM8ka-pVXbNi7zYalm0R6WFBH4X8PQj8C7VfdckGsA6bTBseOVCTbu187_63yU2U7vqYiqwSLmkrBVAJjYMJY_XXfncxwqDWR_aa7eIJSKh22H_6yz6kFyF1h_ZSk68CPAEQpvd9VFAr4VLEwD32Ag6MwymSOxmFWJyddEtttdGcXLSrHcya3RWyG5KAW3Ti-HgNC-xo_C5LgEsUgjeUq-rc8NBXZrNCY-LJ_R-qtB_-5NkwlMJ_fUMBDcmZuciNOH71q7xyn0FGmGjrJXnyVJwyDiTrKRO36piMuiaJE2nIRJaLvhDN5M1K2VhSKPuaqUPyxLzBw"
+                ],
+                "-----BEGIN PUBLIC KEY-----" . PHP_EOL
+                . "MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAvdv73smpkrTIBSM8ka+p" . PHP_EOL
+                . "VXbNi7zYalm0R6WFBH4X8PQj8C7VfdckGsA6bTBseOVCTbu187/63yU2U7vqYiqw" . PHP_EOL
+                . "SLmkrBVAJjYMJY/XXfncxwqDWR/aa7eIJSKh22H/6yz6kFyF1h/ZSk68CPAEQpvd" . PHP_EOL
+                . "9VFAr4VLEwD32Ag6MwymSOxmFWJyddEtttdGcXLSrHcya3RWyG5KAW3Ti+HgNC+x" . PHP_EOL
+                . "o/C5LgEsUgjeUq+rc8NBXZrNCY+LJ/R+qtB/+5NkwlMJ/fUMBDcmZuciNOH71q7x" . PHP_EOL
+                . "yn0FGmGjrJXnyVJwyDiTrKRO36piMuiaJE2nIRJaLvhDN5M1K2VhSKPuaqUPyxLz" . PHP_EOL
+                . "BwIDAQAB" . PHP_EOL
+                . "-----END PUBLIC KEY-----"
+            ]
+        ];
+    }
+}