diff --git a/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php b/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php
index e2cc87bc9..bfe1399f0 100644
--- a/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ArchiveDownloaderTest.php
@@ -16,6 +16,7 @@ use Composer\Test\TestCase;
 
 class ArchiveDownloaderTest extends TestCase
 {
+    /** @var \Composer\Config&\PHPUnit\Framework\MockObject\MockObject */
     protected $config;
 
     public function testGetFileName()
diff --git a/tests/Composer/Test/Downloader/DownloadManagerTest.php b/tests/Composer/Test/Downloader/DownloadManagerTest.php
index 4253882b6..00037f0e5 100644
--- a/tests/Composer/Test/Downloader/DownloadManagerTest.php
+++ b/tests/Composer/Test/Downloader/DownloadManagerTest.php
@@ -17,7 +17,10 @@ use Composer\Test\TestCase;
 
 class DownloadManagerTest extends TestCase
 {
+    /** @var \Composer\Util\Filesystem&\PHPUnit\Framework\MockObject\MockObject */
     protected $filesystem;
+
+    /** @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject */
     protected $io;
 
     public function setUp()
@@ -1091,12 +1094,18 @@ class DownloadManagerTest extends TestCase
         $manager->download($package, 'target_dir');
     }
 
+    /**
+     * @return \Composer\Downloader\DownloaderInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     private function createDownloaderMock()
     {
         return $this->getMockBuilder('Composer\Downloader\DownloaderInterface')
             ->getMock();
     }
 
+    /**
+     * @return \Composer\Package\PackageInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     private function createPackageMock()
     {
         return $this->getMockBuilder('Composer\Package\PackageInterface')
diff --git a/tests/Composer/Test/Downloader/FileDownloaderTest.php b/tests/Composer/Test/Downloader/FileDownloaderTest.php
index 036410407..7ad59b30d 100644
--- a/tests/Composer/Test/Downloader/FileDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FileDownloaderTest.php
@@ -25,13 +25,30 @@ use Composer\Util\Loop;
 
 class FileDownloaderTest extends TestCase
 {
+    /** @var \Composer\Util\HttpDownloader&\PHPUnit\Framework\MockObject\MockObject */
     private $httpDownloader;
+    /** @var \Composer\Config&\PHPUnit\Framework\MockObject\MockObject */
     private $config;
 
+    public function setUp()
+    {
+        $this->httpDownloader = $this->getMockBuilder('Composer\Util\HttpDownloader')->disableOriginalConstructor()->getMock();
+        $this->config = $this->getMockBuilder('Composer\Config')->getMock();
+    }
+
+    /**
+     * @param \Composer\IO\IOInterface $io
+     * @param \Composer\Config&\PHPUnit\Framework\MockObject\MockObject $config
+     * @param \Composer\EventDispatcher\EventDispatcher $eventDispatcher
+     * @param \Composer\Cache $cache
+     * @param \Composer\Util\HttpDownloader&\PHPUnit\Framework\MockObject\MockObject $httpDownloader
+     * @param \Composer\Util\Filesystem $filesystem
+     * @return \Composer\Downloader\FileDownloader
+     */
     protected function getDownloader($io = null, $config = null, $eventDispatcher = null, $cache = null, $httpDownloader = null, $filesystem = null)
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
-        $this->config = $config ?: $this->getMockBuilder('Composer\Config')->getMock();
+        $config = $config ?: $this->config;
         $httpDownloader = $httpDownloader ?: $this->getMockBuilder('Composer\Util\HttpDownloader')->disableOriginalConstructor()->getMock();
         $httpDownloader
             ->expects($this->any())
@@ -166,7 +183,6 @@ class FileDownloaderTest extends TestCase
         $self = $this;
 
         $path = $this->getUniqueTmpDirectory();
-        $config = new Config(false, $path);
 
         $packageMock = $this->getMockBuilder('Composer\Package\PackageInterface')->getMock();
         $packageMock->expects($this->any())
@@ -187,7 +203,16 @@ class FileDownloaderTest extends TestCase
             ->will($this->returnValue($rootPackageMock));
         $composerMock->expects($this->any())
             ->method('getConfig')
-            ->will($this->returnValue($config));
+            ->will($this->returnValue($this->config));
+        $this->config->expects($this->any())
+            ->method('get')
+            ->will($this->returnCallback(function ($key) use ($path) {
+                if ($key === 'vendor-dir') {
+                    return $path.'/vendor';
+                } elseif ($key === 'bin-dir') {
+                    return $path.'/vendor/bin';
+                }
+            }));
 
         $expectedUrl = 'foobar';
         $expectedCacheKey = '/'.sha1($expectedUrl).'.';
@@ -233,7 +258,7 @@ class FileDownloaderTest extends TestCase
                 );
             }));
 
-        $downloader = $this->getDownloader(null, $config, $dispatcher, $cacheMock, $httpDownloaderMock);
+        $downloader = $this->getDownloader(null, $this->config, $dispatcher, $cacheMock, $httpDownloaderMock);
 
         try {
             $loop = new Loop($this->httpDownloader);
@@ -259,7 +284,6 @@ class FileDownloaderTest extends TestCase
         $self = $this;
 
         $path = $this->getUniqueTmpDirectory();
-        $config = new Config(false, $path);
 
         $packageMock = $this->getMockBuilder('Composer\Package\PackageInterface')->getMock();
         $packageMock->expects($this->any())
@@ -280,7 +304,16 @@ class FileDownloaderTest extends TestCase
             ->will($this->returnValue($rootPackageMock));
         $composerMock->expects($this->any())
             ->method('getConfig')
-            ->will($this->returnValue($config));
+            ->will($this->returnValue($this->config));
+        $this->config->expects($this->any())
+            ->method('get')
+            ->will($this->returnCallback(function ($key) use ($path) {
+                if ($key === 'vendor-dir') {
+                    return $path.'/vendor';
+                } elseif ($key === 'bin-dir') {
+                    return $path.'/vendor/bin';
+                }
+            }));
 
         $expectedUrl = 'url';
         $customCacheKey = 'xyzzy';
@@ -327,7 +360,7 @@ class FileDownloaderTest extends TestCase
                 );
             }));
 
-        $downloader = $this->getDownloader(null, $config, $dispatcher, $cacheMock, $httpDownloaderMock);
+        $downloader = $this->getDownloader(null, $this->config, $dispatcher, $cacheMock, $httpDownloaderMock);
 
         try {
             $loop = new Loop($this->httpDownloader);
@@ -352,13 +385,13 @@ class FileDownloaderTest extends TestCase
     {
         $expectedTtl = '99999999';
 
-        $configMock = $this->getMockBuilder('Composer\Config')->getMock();
-        $configMock
+        $this->config = $this->getMockBuilder('Composer\Config')->getMock();
+        $this->config
             ->expects($this->at(0))
             ->method('get')
             ->with('cache-files-ttl')
             ->will($this->returnValue($expectedTtl));
-        $configMock
+        $this->config
             ->expects($this->at(1))
             ->method('get')
             ->with('cache-files-maxsize')
@@ -376,7 +409,7 @@ class FileDownloaderTest extends TestCase
             ->method('gc')
             ->with($expectedTtl, $this->anything());
 
-        $downloader = $this->getDownloader(null, $configMock, null, $cacheMock, null, null);
+        $downloader = $this->getDownloader(null, $this->config, null, $cacheMock, null, null);
     }
 
     public function testDownloadFileWithInvalidChecksum()
diff --git a/tests/Composer/Test/Downloader/FossilDownloaderTest.php b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
index 41611a459..f78e925e8 100644
--- a/tests/Composer/Test/Downloader/FossilDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
@@ -35,6 +35,12 @@ class FossilDownloaderTest extends TestCase
         }
     }
 
+    /**
+     * @param \Composer\IO\IOInterface $io
+     * @param \Composer\Config $config
+     * @param \Composer\Test\Mock\ProcessExecutorMock $executor
+     * @param \Composer\Util\Filesystem $filesystem
+     */
     protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null)
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
diff --git a/tests/Composer/Test/Downloader/GitDownloaderTest.php b/tests/Composer/Test/Downloader/GitDownloaderTest.php
index bfdefe055..ac3e62221 100644
--- a/tests/Composer/Test/Downloader/GitDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/GitDownloaderTest.php
@@ -45,6 +45,10 @@ class GitDownloaderTest extends TestCase
         $this->initGitVersion(false);
     }
 
+    /**
+     * @param string|bool $version
+     * @return void
+     */
     private function initGitVersion($version)
     {
         // reset the static version cache
@@ -53,6 +57,10 @@ class GitDownloaderTest extends TestCase
         $refl->setValue(null, $version);
     }
 
+    /**
+     * @param ?\Composer\Config $config
+     * @return \Composer\Config
+     */
     protected function setupConfig($config = null)
     {
         if (!$config) {
@@ -66,6 +74,12 @@ class GitDownloaderTest extends TestCase
         return $config;
     }
 
+    /**
+     * @param \Composer\IO\IOInterface $io
+     * @param \Composer\Config $config
+     * @param \Composer\Test\Mock\ProcessExecutorMock $executor
+     * @param \Composer\Util\Filesystem $filesystem
+     */
     protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null)
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
@@ -641,6 +655,10 @@ composer https://github.com/old/url (push)
         $this->assertEquals('source', $downloader->getInstallationSource());
     }
 
+    /**
+     * @param string $cmd
+     * @return string
+     */
     private function winCompat($cmd)
     {
         if (Platform::isWindows()) {
diff --git a/tests/Composer/Test/Downloader/HgDownloaderTest.php b/tests/Composer/Test/Downloader/HgDownloaderTest.php
index 19b5b723c..871e3b870 100644
--- a/tests/Composer/Test/Downloader/HgDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/HgDownloaderTest.php
@@ -35,6 +35,12 @@ class HgDownloaderTest extends TestCase
         }
     }
 
+    /**
+     * @param \Composer\IO\IOInterface $io
+     * @param \Composer\Config $config
+     * @param \Composer\Test\Mock\ProcessExecutorMock $executor
+     * @param \Composer\Util\Filesystem $filesystem
+     */
     protected function getDownloaderMock($io = null, $config = null, $executor = null, $filesystem = null)
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
diff --git a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
index cd47d8ecf..95bf048d3 100644
--- a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
@@ -26,14 +26,21 @@ use Composer\Test\Mock\ProcessExecutorMock;
  */
 class PerforceDownloaderTest extends TestCase
 {
+    /** @var \Composer\Config */
     protected $config;
-    /** @var ?PerforceDownloader */
+    /** @var \Composer\Downloader\PerforceDownloader */
     protected $downloader;
+    /** @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject */
     protected $io;
+    /** @var \Composer\Package\PackageInterface&\PHPUnit\Framework\MockObject\MockObject */
     protected $package;
+    /** @var \Composer\Test\Mock\ProcessExecutorMock */
     protected $processExecutor;
+    /** @var string[] */
     protected $repoConfig;
+    /** @var \Composer\Repository\VcsRepository&\PHPUnit\Framework\MockObject\MockObject */
     protected $repository;
+    /** @var string */
     protected $testPath;
 
     protected function setUp()
@@ -48,20 +55,9 @@ class PerforceDownloaderTest extends TestCase
         $this->downloader = new PerforceDownloader($this->io, $this->config, $this->processExecutor);
     }
 
-    protected function tearDown()
-    {
-        $this->downloader = null;
-        $this->package = null;
-        $this->repository = null;
-        $this->io = null;
-        $this->config = null;
-        $this->repoConfig = null;
-        if (is_dir($this->testPath)) {
-            $fs = new Filesystem;
-            $fs->removeDirectory($this->testPath);
-        }
-    }
-
+    /**
+     * @return \Composer\Config
+     */
     protected function getConfig()
     {
         $config = new Config();
@@ -71,11 +67,17 @@ class PerforceDownloaderTest extends TestCase
         return $config;
     }
 
+    /**
+     * @return \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     protected function getMockIoInterface()
     {
         return $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
     }
 
+    /**
+     * @return \Composer\Package\PackageInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     protected function getMockPackageInterface(VcsRepository $repository)
     {
         $package = $this->getMockBuilder('Composer\Package\PackageInterface')->getMock();
@@ -84,11 +86,20 @@ class PerforceDownloaderTest extends TestCase
         return $package;
     }
 
+    /**
+     * @return string[]
+     */
     protected function getRepoConfig()
     {
         return array('url' => 'TEST_URL', 'p4user' => 'TEST_USER');
     }
 
+    /**
+     * @param string[] $repoConfig
+     * @param \Composer\IO\IOInterface $io
+     * @param \Composer\Config $config
+     * @return \Composer\Repository\VcsRepository&\PHPUnit\Framework\MockObject\MockObject
+     */
     protected function getMockRepository(array $repoConfig, IOInterface $io, Config $config)
     {
         $repository = $this->getMockBuilder('Composer\Repository\VcsRepository')
diff --git a/tests/Composer/Test/Downloader/ZipDownloaderTest.php b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
index 9c9c974fd..b8e148f2b 100644
--- a/tests/Composer/Test/Downloader/ZipDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/ZipDownloaderTest.php
@@ -21,13 +21,15 @@ use Composer\Util\Loop;
 
 class ZipDownloaderTest extends TestCase
 {
-    /**
-     * @var string
-     */
+    /** @var string */
     private $testDir;
+    /** @var \Composer\Util\HttpDownloader */
     private $httpDownloader;
+    /** @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject */
     private $io;
+    /** @var \Composer\Config&\PHPUnit\Framework\MockObject\MockObject */
     private $config;
+    /** @var \Composer\Package\PackageInterface&\PHPUnit\Framework\MockObject\MockObject */
     private $package;
 
     public function setUp()
@@ -47,6 +49,12 @@ class ZipDownloaderTest extends TestCase
         $this->setPrivateProperty('hasZipArchive', null);
     }
 
+    /**
+     * @param string $name
+     * @param mixed $value
+     * @param ?\Composer\Test\Downloader\MockedZipDownloader $obj
+     * @return void
+     */
     public function setPrivateProperty($name, $value, $obj = null)
     {
         $reflectionClass = new \ReflectionClass('Composer\Downloader\ZipDownloader');
@@ -296,6 +304,10 @@ class ZipDownloaderTest extends TestCase
         $this->wait($promise);
     }
 
+    /**
+     * @param ?\React\Promise\PromiseInterface $promise
+     * @return void
+     */
     private function wait($promise)
     {
         if (null === $promise) {