diff --git a/composer.json b/composer.json
index 2504c7d..42b0a93 100644
--- a/composer.json
+++ b/composer.json
@@ -8,18 +8,18 @@
         "email": "me@stephencoakley.com"
     }],
     "require": {
-        "php": ">=5.5",
+        "php": ">=7.3",
         "mpociot/phpws": "^2.0",
         "evenement/evenement": "~3.0",
-        "guzzlehttp/guzzle": "~6.0",
+        "guzzlehttp/guzzle": "~6.0|~7.0",
         "react/event-loop": "^1.0 || ^0.5 || ^0.4",
         "react/promise": "^2.2",
         "react/promise-timer": "^1.2.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "~4.6",
-        "fzaninotto/faker": "~1.4",
-        "apigen/apigen": "^4.1"
+        "phpunit/phpunit": "~9.4",
+        "apigen/apigen": "^4.1",
+        "fakerphp/faker": "^1.13"
     },
     "autoload": {
         "psr-4": {
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 651dbbe..59493a3 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -1,13 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<phpunit bootstrap="vendor/autoload.php" colors="true">
-    <testsuites>
-        <testsuite name="slack-client">
-            <directory>tests</directory>
-        </testsuite>
-    </testsuites>
-    <filter>
-        <whitelist>
-            <directory>src</directory>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" bootstrap="vendor/autoload.php" colors="true" xsi:noNamespaceSchemaLocation="https://schema.phpunit.de/9.3/phpunit.xsd">
+  <coverage>
+    <include>
+      <directory>src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="slack-client">
+      <directory>tests</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>
diff --git a/tests/Message/MessageBuilderTest.php b/tests/Message/MessageBuilderTest.php
index 2b3eeb7..33163a1 100644
--- a/tests/Message/MessageBuilderTest.php
+++ b/tests/Message/MessageBuilderTest.php
@@ -12,7 +12,7 @@ class MessageBuilderTest extends TestCase
 {
     protected $builder;
 
-    public function setUp()
+    public function setUp(): void
     {
         parent::setUp();
 
diff --git a/tests/TestCase.php b/tests/TestCase.php
index 9e8ef36..6a32e31 100644
--- a/tests/TestCase.php
+++ b/tests/TestCase.php
@@ -6,6 +6,7 @@
 use GuzzleHttp\HandlerStack;
 use GuzzleHttp\Middleware;
 use GuzzleHttp\Psr7\Response;
+use PHPUnit\Framework\TestCase as BaseTestcase;
 use React\EventLoop\Factory;
 use React\Promise\ExtendedPromiseInterface;
 use Slack\ApiClient;
@@ -13,7 +14,7 @@
 /**
  * Base helper class for test cases for mocking API requests and responses.
  */
-abstract class TestCase extends \PHPUnit_Framework_TestCase
+abstract class TestCase extends BaseTestcase
 {
     /**
      * @var \Faker\Generator A Faker fake data generator.
@@ -53,7 +54,7 @@ abstract class TestCase extends \PHPUnit_Framework_TestCase
     /**
      * Sets up a test with some useful mock objects.
      */
-    public function setUp()
+    public function setUp(): void
     {
         // Create a mock handler
         $this->mock = new MockHandler();
@@ -83,7 +84,7 @@ public function setUp()
     /**
      * Works in conjunction with watchPromise() to unwrap promise exceptions.
      */
-    public function tearDown()
+    public function tearDown(): void
     {
         $this->loop->run();