diff --git a/composer.json b/composer.json
index d4cb8e9a3..2cbbc6aac 100644
--- a/composer.json
+++ b/composer.json
@@ -40,7 +40,7 @@
         "composer/pcre": "^1.0"
     },
     "require-dev": {
-        "symfony/phpunit-bridge": "^5.4 || ^6.0",
+        "symfony/phpunit-bridge": "^6.0",
         "phpspec/prophecy": "^1.10",
         "phpstan/phpstan": "^1.0",
         "phpstan/phpstan-phpunit": "^1.0",
@@ -84,10 +84,7 @@
     ],
     "scripts": {
         "compile": "@php -dphar.readonly=0 bin/compile",
-        "test": [
-            "@putenv SYMFONY_PHPUNIT_VERSION=8.5",
-            "@php simple-phpunit"
-        ],
+        "test": "@php simple-phpunit",
         "phpstan": "@php vendor/bin/phpstan analyse --configuration=phpstan/config.neon"
     },
     "scripts-descriptions": {
diff --git a/composer.lock b/composer.lock
index 3b94b9783..a8a5857b0 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at https://getcomposer.org/doc/01-basic-usage.md#installing-dependencies",
         "This file is @generated automatically"
     ],
-    "content-hash": "b75018840aa186f02f947abb15a39369",
+    "content-hash": "84679af67d11fbadffda53328d7fe1b7",
     "packages": [
         {
             "name": "composer/ca-bundle",
@@ -3799,5 +3799,5 @@
     "platform-overrides": {
         "php": "7.2.5"
     },
-    "plugin-api-version": "2.3.0"
+    "plugin-api-version": "2.1.0"
 }
diff --git a/src/Composer/Command/GlobalCommand.php b/src/Composer/Command/GlobalCommand.php
index ad629de4b..91aae03f0 100644
--- a/src/Composer/Command/GlobalCommand.php
+++ b/src/Composer/Command/GlobalCommand.php
@@ -62,10 +62,9 @@ EOT
     }
 
     /**
-     * @return int|void
      * @throws \Symfony\Component\Console\Exception\ExceptionInterface
      */
-    public function run(InputInterface $input, OutputInterface $output)
+    public function run(InputInterface $input, OutputInterface $output): int
     {
         if (!method_exists($input, '__toString')) {
             throw new \LogicException('Expected an Input instance that is stringable, got '.get_class($input));
diff --git a/src/Composer/Console/Application.php b/src/Composer/Console/Application.php
index b5af14af8..cc9f08685 100644
--- a/src/Composer/Console/Application.php
+++ b/src/Composer/Console/Application.php
@@ -119,10 +119,7 @@ class Application extends BaseApplication
         parent::__construct('Composer', Composer::getVersion());
     }
 
-    /**
-     * @return int
-     */
-    public function run(InputInterface $input = null, OutputInterface $output = null)
+    public function run(InputInterface $input = null, OutputInterface $output = null): int
     {
         if (null === $output) {
             $output = Factory::createOutput();
@@ -131,10 +128,7 @@ class Application extends BaseApplication
         return parent::run($input, $output);
     }
 
-    /**
-     * @return int
-     */
-    public function doRun(InputInterface $input, OutputInterface $output)
+    public function doRun(InputInterface $input, OutputInterface $output): int
     {
         $this->disablePluginsByDefault = $input->hasParameterOption('--no-plugins');
         $this->disableScriptsByDefault = $input->hasParameterOption('--no-scripts');
@@ -483,10 +477,7 @@ class Application extends BaseApplication
         return $this->io;
     }
 
-    /**
-     * @return string
-     */
-    public function getHelp()
+    public function getHelp(): string
     {
         return self::$logo . parent::getHelp();
     }
@@ -495,7 +486,7 @@ class Application extends BaseApplication
      * Initializes all the composer commands.
      * @return \Symfony\Component\Console\Command\Command[]
      */
-    protected function getDefaultCommands()
+    protected function getDefaultCommands(): array
     {
         $commands = array_merge(parent::getDefaultCommands(), array(
             new Command\AboutCommand(),
@@ -535,10 +526,7 @@ class Application extends BaseApplication
         return $commands;
     }
 
-    /**
-     * @return string
-     */
-    public function getLongVersion()
+    public function getLongVersion(): string
     {
         if (Composer::BRANCH_ALIAS_VERSION && Composer::BRANCH_ALIAS_VERSION !== '@package_branch_alias_version'.'@') {
             return sprintf(
@@ -553,10 +541,7 @@ class Application extends BaseApplication
         return parent::getLongVersion() . ' ' . Composer::RELEASE_DATE;
     }
 
-    /**
-     * @return InputDefinition
-     */
-    protected function getDefaultInputDefinition()
+    protected function getDefaultInputDefinition(): InputDefinition
     {
         $definition = parent::getDefaultInputDefinition();
         $definition->addOption(new InputOption('--profile', null, InputOption::VALUE_NONE, 'Display timing and memory usage information'));
diff --git a/src/Composer/Console/HtmlOutputFormatter.php b/src/Composer/Console/HtmlOutputFormatter.php
index 7fc0876ec..fcb8fab4b 100644
--- a/src/Composer/Console/HtmlOutputFormatter.php
+++ b/src/Composer/Console/HtmlOutputFormatter.php
@@ -60,12 +60,7 @@ class HtmlOutputFormatter extends OutputFormatter
         parent::__construct(true, $styles);
     }
 
-    /**
-     * @param ?string $message
-     *
-     * @return string
-     */
-    public function format($message)
+    public function format(?string $message): ?string
     {
         $formatted = parent::format($message);
 
diff --git a/src/Composer/IO/BaseIO.php b/src/Composer/IO/BaseIO.php
index 24a0c3b62..33cc14eef 100644
--- a/src/Composer/IO/BaseIO.php
+++ b/src/Composer/IO/BaseIO.php
@@ -159,74 +159,47 @@ abstract class BaseIO implements IOInterface
         ProcessExecutor::setTimeout((int) $config->get('process-timeout'));
     }
 
-    /**
-     * @return void
-     */
-    public function emergency($message, array $context = array())
+    public function emergency($message, array $context = array()): void
     {
         $this->log(LogLevel::EMERGENCY, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function alert($message, array $context = array())
+    public function alert($message, array $context = array()): void
     {
         $this->log(LogLevel::ALERT, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function critical($message, array $context = array())
+    public function critical($message, array $context = array()): void
     {
         $this->log(LogLevel::CRITICAL, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function error($message, array $context = array())
+    public function error($message, array $context = array()): void
     {
         $this->log(LogLevel::ERROR, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function warning($message, array $context = array())
+    public function warning($message, array $context = array()): void
     {
         $this->log(LogLevel::WARNING, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function notice($message, array $context = array())
+    public function notice($message, array $context = array()): void
     {
         $this->log(LogLevel::NOTICE, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function info($message, array $context = array())
+    public function info($message, array $context = array()): void
     {
         $this->log(LogLevel::INFO, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function debug($message, array $context = array())
+    public function debug($message, array $context = array()): void
     {
         $this->log(LogLevel::DEBUG, $message, $context);
     }
 
-    /**
-     * @return void
-     */
-    public function log($level, $message, array $context = array())
+    public function log($level, $message, array $context = array()): void
     {
         if (in_array($level, array(LogLevel::EMERGENCY, LogLevel::ALERT, LogLevel::CRITICAL, LogLevel::ERROR))) {
             $this->writeError('<error>'.$message.'</error>');
diff --git a/tests/Composer/Test/Downloader/ZipDownloaderTest.php b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
index 7e1f33119..3885a33e6 100644
--- a/tests/Composer/Test/Downloader/ZipDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
@@ -114,11 +114,11 @@ class ZipDownloaderTest extends TestCase
 
         $this->setPrivateProperty('hasZipArchive', true);
         $downloader = new MockedZipDownloader($this->io, $this->config, $this->httpDownloader);
-        $zipArchive = $this->getMockBuilder('ZipArchive')->getMock();
-        $zipArchive->expects($this->at(0))
+        $zipArchive = $this->getMockBuilder('ZipArchive')->onlyMethods(['open', 'extractTo'])->getMock();
+        $zipArchive->expects($this->once())
             ->method('open')
             ->will($this->returnValue(true));
-        $zipArchive->expects($this->at(1))
+        $zipArchive->expects($this->once())
             ->method('extractTo')
             ->will($this->returnValue(false));