diff --git a/composer.json b/composer.json
index cfa3040..aed7bf5 100644
--- a/composer.json
+++ b/composer.json
@@ -8,10 +8,11 @@
 		"email": "damian@silverstripe.com"
 	}],
 	"require": {
+		"php": "^7.3 || ^8.0",
 		"silverstripe/comments": "^3.0"
 	},
 	"require-dev": {
-        "sminnee/phpunit": "^5.7",
+        "phpunit/phpunit": "^9.5",
         "squizlabs/php_codesniffer": "^3.0"
     },
     "autoload": {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 0deb46e..1344dac 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,8 +1,9 @@
 <phpunit bootstrap="vendor/silverstripe/cms/tests/bootstrap.php" colors="true">
-    <testsuite name="Default">
-        <directory>tests</directory>
-    </testsuite>
-
+    <testsuites>
+        <testsuite name="Default">
+            <directory>tests</directory>
+        </testsuite>
+    </testsuites>
     <filter>
         <whitelist addUncoveredFilesFromWhitelist="true">
             <directory suffix=".php">src/</directory>
diff --git a/tests/CommentNotifiableTest.php b/tests/CommentNotifiableTest.php
index 1c750a3..b72d7a7 100644
--- a/tests/CommentNotifiableTest.php
+++ b/tests/CommentNotifiableTest.php
@@ -19,7 +19,7 @@ class CommentNotifiableTest extends SapphireTest
         CommentNotifiableTestDataObject::class
     ];
 
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
 
@@ -29,7 +29,7 @@ protected function setUp()
         $_SERVER['HTTP_HOST'] = 'www.mysite.com';
     }
 
-    protected function tearDown()
+    protected function tearDown(): void
     {
         $_SERVER['HTTP_HOST'] = $this->oldhost;
 
diff --git a/tests/CommentNotifierTest.php b/tests/CommentNotifierTest.php
index c5bc584..ffa5608 100644
--- a/tests/CommentNotifierTest.php
+++ b/tests/CommentNotifierTest.php
@@ -24,7 +24,7 @@ class CommentNotifierTest extends SapphireTest
         CommentNotifierTestController::class
     ];
 
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
 
@@ -33,7 +33,7 @@ protected function setUp()
         $_SERVER['HTTP_HOST'] = 'www.mysite.com';
     }
 
-    protected function tearDown()
+    protected function tearDown(): void
     {
         $_SERVER['HTTP_HOST'] = $this->oldhost;
 
@@ -56,9 +56,9 @@ public function testSendEmail()
 
         $email = $this->findEmail('andrew@address.com', 'noreply@mysite.com', 'A new comment has been posted');
 
-        $this->assertContains('<li>Bob Bobberson</li>', $email['Content']);
-        $this->assertContains('<li>bob@address.com</li>', $email['Content']);
-        $this->assertContains('<blockquote>Hey what a lovely comment</blockquote>', $email['Content']);
+        $this->assertStringContainsString('<li>Bob Bobberson</li>', $email['Content']);
+        $this->assertStringContainsString('<li>bob@address.com</li>', $email['Content']);
+        $this->assertStringContainsString('<blockquote>Hey what a lovely comment</blockquote>', $email['Content']);
 
         $this->clearEmails();
 
@@ -67,9 +67,12 @@ public function testSendEmail()
         $this->assertEmailSent('andrew@address.com', 'noreply@mysite.com', 'A new comment has been posted');
 
         $email = $this->findEmail('andrew@address.com', 'noreply@mysite.com', 'A new comment has been posted');
-        $this->assertContains('<li>Secret</li>', $email['Content']);
-        $this->assertContains('<li>secret@notallowed.com</li>', $email['Content']);
-        $this->assertContains('<blockquote>I don&#039;t want to disclose my details</blockquote>', $email['Content']);
+        $this->assertStringContainsString('<li>Secret</li>', $email['Content']);
+        $this->assertStringContainsString('<li>secret@notallowed.com</li>', $email['Content']);
+        $this->assertStringContainsString(
+            '<blockquote>I don&#039;t want to disclose my details</blockquote>',
+            $email['Content']
+        );
 
         $this->clearEmails();
 
@@ -79,9 +82,9 @@ public function testSendEmail()
 
         $email = $this->findEmail('andrew@address.com', 'noreply@mysite.com', 'A new comment has been posted');
 
-        $this->assertContains('<li>Anonymous</li>', $email['Content']);
-        $this->assertContains('<li>notlogged@in.com</li>', $email['Content']);
-        $this->assertContains('<blockquote>I didn&#039;t log in</blockquote>', $email['Content']);
+        $this->assertStringContainsString('<li>Anonymous</li>', $email['Content']);
+        $this->assertStringContainsString('<li>notlogged@in.com</li>', $email['Content']);
+        $this->assertStringContainsString('<blockquote>I didn&#039;t log in</blockquote>', $email['Content']);
 
         $this->clearEmails();