diff --git a/composer.json b/composer.json
index d10082c..6426f07 100644
--- a/composer.json
+++ b/composer.json
@@ -13,7 +13,8 @@
         }
     ],
     "require": {
-        "silverstripe/framework": "^4.2",
+        "php": "^7.3 || ^8.0",
+        "silverstripe/framework": "^4.10",
         "colymba/gridfield-bulk-editing-tools": "^3.0.0-beta4"
     },
     "suggest": {
@@ -21,7 +22,7 @@
         "silverstripe/cms": "The SilverStripe Content Management System"
     },
     "require-dev": {
-        "sminnee/phpunit": "^5.7",
+        "phpunit/phpunit": "^9.5",
         "squizlabs/php_codesniffer": "^3.0"
     },
     "extra": {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index f148411..6470738 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/CommentingControllerTest.php b/tests/CommentingControllerTest.php
index 68d642c..ec48e37 100644
--- a/tests/CommentingControllerTest.php
+++ b/tests/CommentingControllerTest.php
@@ -31,7 +31,7 @@ class CommentingControllerTest extends FunctionalTest
 
     protected $securityEnabled;
 
-    protected function tearDown()
+    protected function tearDown(): void
     {
         if ($this->securityEnabled) {
             SecurityToken::inst()->enable();
@@ -41,7 +41,7 @@ class CommentingControllerTest extends FunctionalTest
         parent::tearDown();
     }
 
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
         $this->securityEnabled = SecurityToken::inst()->is_enabled();
@@ -194,7 +194,7 @@ class CommentingControllerTest extends FunctionalTest
         // specific page
         $response = $this->get('comments/rss/SilverStripe-Comments-Tests-Stubs-CommentableItem/'.$item->ID);
         $this->assertEquals(1, substr_count($response->getBody(), "<item>"));
-        $this->assertContains('<dc:creator>FA</dc:creator>', $response->getBody());
+        $this->assertStringContainsString('<dc:creator>FA</dc:creator>', $response->getBody());
 
         // test accessing comments on a type that doesn't exist
         $response = $this->get('comments/rss/Fake');
diff --git a/tests/CommentsExtensionTest.php b/tests/CommentsExtensionTest.php
index 5fc5226..87bcadb 100644
--- a/tests/CommentsExtensionTest.php
+++ b/tests/CommentsExtensionTest.php
@@ -32,7 +32,7 @@ class CommentsExtensionTest extends FunctionalTest
         ],
     ];
 
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
 
@@ -262,44 +262,44 @@ class CommentsExtensionTest extends FunctionalTest
         $item = $this->objFromFixture(CommentableItem::class, 'first');
 
         // The comments form is HTML to do assertions by contains
-        $cf = $item->CommentsForm();
+        $cf = (string) $item->CommentsForm();
         $expected = '/comments/CommentsForm/" method="post" enctype="application/x-www-form-urlencoded">';
 
-        $this->assertContains($expected, $cf);
-        $this->assertContains('<h4>Post your comment</h4>', $cf);
+        $this->assertStringContainsString($expected, $cf);
+        $this->assertStringContainsString('<h4>Post your comment</h4>', $cf);
         // check the comments form exists
         $expected = '<input type="text" name="Name"';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<input type="email" name="Email"';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<input type="text" name="URL"';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<input type="hidden" name="ParentID"';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<textarea name="Comment"';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<input type="submit" name="action_doPostComment" value="Post" class="action"';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '/comments/spam/';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<p>Reply to firstComA 1</p>';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '/comments/delete';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<p>Reply to firstComA 2</p>';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
 
         $expected = '<p>Reply to firstComA 3</p>';
-        $this->assertContains($expected, $cf);
+        $this->assertStringContainsString($expected, $cf);
     }
 
     public function testAttachedToSiteTree()
diff --git a/tests/CommentsGridFieldActionTest.php b/tests/CommentsGridFieldActionTest.php
index 8558df2..e044480 100644
--- a/tests/CommentsGridFieldActionTest.php
+++ b/tests/CommentsGridFieldActionTest.php
@@ -37,7 +37,7 @@ class CommentsGridFieldActionTest extends SapphireTest
     /** @var Form */
     protected $form;
 
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
         $this->list = new DataList(Team::class);
@@ -96,27 +96,27 @@ class CommentsGridFieldActionTest extends SapphireTest
         $record->write();
         $recordID = $record->ID;
         $html = $action->getColumnContent($this->gridField, $record, Comment::class);
-        $this->assertContains('data-url="admin/comments/mockform/field/testfield', $html);
+        $this->assertStringContainsString('data-url="admin/comments/mockform/field/testfield', $html);
 
-        $this->assertContains('value="Spam"', $html);
-        $this->assertContains('id="action_CustomAction' . $recordID . 'Spam"', $html);
+        $this->assertStringContainsString('value="Spam"', $html);
+        $this->assertStringContainsString('id="action_CustomAction' . $recordID . 'Spam"', $html);
 
-        $this->assertContains('value="Approve"', $html);
-        $this->assertContains('id="action_CustomAction' . $recordID . 'Approve"', $html);
+        $this->assertStringContainsString('value="Approve"', $html);
+        $this->assertStringContainsString('id="action_CustomAction' . $recordID . 'Approve"', $html);
 
         // If marked as spam, only the approve button should be available
         $record->markSpam();
         $record->write();
         $html = $action->getColumnContent($this->gridField, $record, Comment::class);
-        $this->assertContains('value="Approve"', $html);
-        $this->assertNotContains('value="Spam"', $html);
+        $this->assertStringContainsString('value="Approve"', $html);
+        $this->assertStringNotContainsString('value="Spam"', $html);
 
         // If marked as spam, only the approve button should be available
         $record->markApproved();
         $record->write();
         $html = $action->getColumnContent($this->gridField, $record, Comment::class);
-        $this->assertNotContains('value="Approve"', $html);
-        $this->assertContains('value="Spam"', $html);
+        $this->assertStringNotContainsString('value="Approve"', $html);
+        $this->assertStringContainsString('value="Spam"', $html);
     }
 
     public function testGetActions()
diff --git a/tests/CommentsTest.php b/tests/CommentsTest.php
index 027ca59..6d213a8 100644
--- a/tests/CommentsTest.php
+++ b/tests/CommentsTest.php
@@ -26,7 +26,7 @@ class CommentsTest extends FunctionalTest
         CommentableItemDisabled::class,
     ];
 
-    protected function setUp()
+    protected function setUp(): void
     {
         parent::setUp();
 
@@ -235,7 +235,7 @@ class CommentsTest extends FunctionalTest
         $comment = $this->objFromFixture(Comment::class, 'firstComA');
         $commentID = $comment->ID;
         $adminComment1Link = $comment->DeleteLink();
-        $this->assertContains('comments/delete/' . $commentID . '?t=', $adminComment1Link);
+        $this->assertStringContainsString('comments/delete/' . $commentID . '?t=', $adminComment1Link);
 
         // Test that this link can't be shared / XSS exploited
         $this->logInAs('commentadmin2');
@@ -275,7 +275,7 @@ class CommentsTest extends FunctionalTest
         $comment = $this->objFromFixture(Comment::class, 'firstComA');
         $commentID = $comment->ID;
         $adminComment1Link = $comment->SpamLink();
-        $this->assertContains('comments/spam/' . $commentID . '?t=', $adminComment1Link);
+        $this->assertStringContainsString('comments/spam/' . $commentID . '?t=', $adminComment1Link);
 
         // Test that this link can't be shared / XSS exploited
         $this->logInAs('commentadmin2');
@@ -318,7 +318,7 @@ class CommentsTest extends FunctionalTest
         $comment = $this->objFromFixture(Comment::class, 'secondComC');
         $commentID = $comment->ID;
         $adminComment1Link = $comment->HamLink();
-        $this->assertContains('comments/ham/' . $commentID . '?t=', $adminComment1Link);
+        $this->assertStringContainsString('comments/ham/' . $commentID . '?t=', $adminComment1Link);
 
         // Test that this link can't be shared / XSS exploited
         $this->logInAs('commentadmin2');
@@ -361,7 +361,7 @@ class CommentsTest extends FunctionalTest
         $comment = $this->objFromFixture(Comment::class, 'secondComB');
         $commentID = $comment->ID;
         $adminComment1Link = $comment->ApproveLink();
-        $this->assertContains('comments/approve/' . $commentID . '?t=', $adminComment1Link);
+        $this->assertStringContainsString('comments/approve/' . $commentID . '?t=', $adminComment1Link);
 
         // Test that this link can't be shared / XSS exploited
         $this->logInAs('commentadmin2');
@@ -775,30 +775,30 @@ class CommentsTest extends FunctionalTest
         $method = $this->getMethod('ActionLink');
 
         // test with starts of strings and tokens and salts change each time
-        $this->assertContains(
+        $this->assertStringContainsString(
             '/comments/theaction/' . $comment->ID,
             $method->invokeArgs($comment, array('theaction'))
         );
 
-        $this->assertContains(
+        $this->assertStringContainsString(
             '/comments/delete/' . $comment->ID,
             $comment->DeleteLink()
         );
 
-        $this->assertContains(
+        $this->assertStringContainsString(
             '/comments/spam/' . $comment->ID,
             $comment->SpamLink()
         );
 
         $comment->markSpam();
-        $this->assertContains(
+        $this->assertStringContainsString(
             '/comments/ham/' . $comment->ID,
             $comment->HamLink()
         );
 
         //markApproved
         $comment->markUnapproved();
-        $this->assertContains(
+        $this->assertStringContainsString(
             '/comments/approve/' . $comment->ID,
             $comment->ApproveLink()
         );