diff --git a/.gitignore b/.gitignore
index af1f417..8560273 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,3 @@
+.phpunit.result.cache
 composer.lock
 /vendor
diff --git a/composer.json b/composer.json
index 7533371..d5a35e3 100644
--- a/composer.json
+++ b/composer.json
@@ -15,11 +15,12 @@
     "require": {
         "php": "^7.4 || ^8.0",
         "lib-openssl": "*",
-        "composer/ca-bundle": "^1.2"
+        "composer/ca-bundle": "^1.2",
+        "ext-openssl": "*"
     },
 
     "require-dev": {
-        "phpunit/phpunit": "^5",
+        "phpunit/phpunit": "^9.0",
         "php-vfs/php-vfs": "^1.3"
     },
 
diff --git a/phpunit.xml b/phpunit.xml
index c0377f3..8b22088 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,13 +1,8 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <phpunit>
     <testsuites>
-        <testsuite>
+        <testsuite name="Tests">
             <directory>tests/</directory>
         </testsuite>
     </testsuites>
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">src</directory>
-        </whitelist>
-    </filter>
-</phpunit>
\ No newline at end of file
+</phpunit>
diff --git a/src/Punkstar/Ssl/Certificate.php b/src/Punkstar/Ssl/Certificate.php
index 6fa8699..a802287 100644
--- a/src/Punkstar/Ssl/Certificate.php
+++ b/src/Punkstar/Ssl/Certificate.php
@@ -156,6 +156,10 @@ public function signedBy(Certificate $cert): bool
 
     protected function extractCertData($certificate): array
     {
+        if (null === $certificate) {
+            throw new Exception("Unable to extract data from certificate.", Exception::MALFORMED_CERTIFICATE);
+        }
+
         $parsedData = openssl_x509_parse($certificate);
 
         if ($parsedData === false) {
diff --git a/src/Punkstar/Ssl/Exception.php b/src/Punkstar/Ssl/Exception.php
index 8d327d3..21a58b6 100644
--- a/src/Punkstar/Ssl/Exception.php
+++ b/src/Punkstar/Ssl/Exception.php
@@ -9,4 +9,4 @@ class Exception extends \Exception
     const MALFORMED_CERTIFICATE = 2001;
 
     const CONNECTION_PROBLEM = 3001;
-}
\ No newline at end of file
+}
diff --git a/tests/Punkstar/SslTest/IntegrationTest.php b/tests/Punkstar/SslTest/IntegrationTest.php
index b21b860..f94147a 100644
--- a/tests/Punkstar/SslTest/IntegrationTest.php
+++ b/tests/Punkstar/SslTest/IntegrationTest.php
@@ -16,15 +16,15 @@ public function testExampleCerts($certFileName)
         $reader = new Reader();
         $cert = $reader->readFromFile($certFileName);
 
-        $this->assertInternalType('string', $cert->certName());
-        $this->assertInternalType('string', $cert->toString());
-        $this->assertInternalType('string', (string) $cert);
+        $this->assertIsString($cert->certName());
+        $this->assertIsString($cert->toString());
+        $this->assertIsString((string) $cert);
         $this->assertInstanceOf('DateTime', $cert->validTo());
         $this->assertInstanceOf('DateTime', $cert->validFrom());
-        $this->assertInternalType('array', $cert->subject());
-        $this->assertInternalType('array', $cert->issuer());
-        $this->assertInternalType('array', $cert->sans());
-        $this->assertInternalType('string', $cert->signatureAlgorithm());
+        $this->assertIsArray($cert->subject());
+        $this->assertIsArray($cert->issuer());
+        $this->assertIsArray($cert->sans());
+        $this->assertIsString($cert->signatureAlgorithm());
     }
 
     /**
diff --git a/tests/Punkstar/SslTest/Parser/SanParserTest.php b/tests/Punkstar/SslTest/Parser/SanParserTest.php
index 77fbe0c..eb85d9f 100644
--- a/tests/Punkstar/SslTest/Parser/SanParserTest.php
+++ b/tests/Punkstar/SslTest/Parser/SanParserTest.php
@@ -80,7 +80,7 @@ public function testParse()
         $sanParser = new SanParser();
         $result = $sanParser->parse($input);
 
-        $this->assertInternalType('array', $result);
+        $this->assertIsArray($result);
         $this->assertCount(count($output), $result);
 
         foreach ($output as $outputItem) {
diff --git a/tests/Punkstar/SslTest/ReaderTest.php b/tests/Punkstar/SslTest/ReaderTest.php
index 161a241..97a847d 100644
--- a/tests/Punkstar/SslTest/ReaderTest.php
+++ b/tests/Punkstar/SslTest/ReaderTest.php
@@ -3,6 +3,7 @@
 namespace Punkstar\SslTest;
 
 use PHPUnit\Framework\TestCase;
+use Punkstar\Ssl\Exception;
 use Punkstar\Ssl\Reader;
 use VirtualFileSystem\FileSystem;
 
@@ -10,26 +11,28 @@ class ReaderTest extends TestCase
 {
     /**
      * @test
-     * @expectedException \Punkstar\Ssl\Exception
-     * @expectedExceptionCode 1001
      */
     public function testFileNotFound()
     {
+        $this->expectException(Exception::class);
+        $this->expectExceptionCode(1001);
+
         $reader = new Reader();
         $reader->readFromFile("idontexist.tstst.stst.stst");
     }
 
     /**
      * @test
-     * @expectedException \Punkstar\Ssl\Exception
-     * @expectedExceptionCode 2001
      */
     public function testJunkCert()
     {
+        $this->expectException(Exception::class);
+        $this->expectExceptionCode(2001);
+
         $fs = new FileSystem();
         $fs->createFile("/junk.crt", "junk-content");
 
         $reader = new Reader();
         $reader->readFromFile($fs->path("/junk.crt"));
     }
-}
\ No newline at end of file
+}