diff --git a/src/Composer/Autoload/AutoloadGenerator.php b/src/Composer/Autoload/AutoloadGenerator.php
index 138b111d6..c79076c21 100644
--- a/src/Composer/Autoload/AutoloadGenerator.php
+++ b/src/Composer/Autoload/AutoloadGenerator.php
@@ -719,7 +719,7 @@ EOF;
             $package = $item[0];
             foreach (array_merge($package->getReplaces(), $package->getProvides()) as $link) {
                 if (preg_match('{^ext-(.+)$}iD', $link->getTarget(), $match)) {
-                    $extensionProviders[$match[1]][] = $link->getConstraint() ?: new MatchAllConstraint();
+                    $extensionProviders[$match[1]][] = $link->getConstraint();
                 }
             }
         }
@@ -736,7 +736,8 @@ EOF;
                     continue;
                 }
 
-                if ('php' === $link->getTarget() && ($constraint = $link->getConstraint())) {
+                if ('php' === $link->getTarget()) {
+                    $constraint = $link->getConstraint();
                     if ($constraint->getLowerBound()->compareTo($lowestPhpVersion, '>')) {
                         $lowestPhpVersion = $constraint->getLowerBound();
                     }
@@ -746,7 +747,7 @@ EOF;
                     // skip extension checks if they have a valid provider/replacer
                     if (isset($extensionProviders[$match[1]])) {
                         foreach ($extensionProviders[$match[1]] as $provided) {
-                            if (!$link->getConstraint() || $provided->matches($link->getConstraint())) {
+                            if ($provided->matches($link->getConstraint())) {
                                 continue 2;
                             }
                         }
diff --git a/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php b/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php
index de6dba023..f0321a42c 100644
--- a/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php
+++ b/tests/Composer/Test/DependencyResolver/RuleSetIteratorTest.php
@@ -22,7 +22,9 @@ use Composer\Test\TestCase;
 
 class RuleSetIteratorTest extends TestCase
 {
+    /** @var array<RuleSet::TYPE_*, Rule[]> */
     protected $rules;
+    /** @var Pool */
     protected $pool;
 
     protected function setUp()
diff --git a/tests/Composer/Test/DependencyResolver/SolverTest.php b/tests/Composer/Test/DependencyResolver/SolverTest.php
index 712b2b108..629a399a3 100644
--- a/tests/Composer/Test/DependencyResolver/SolverTest.php
+++ b/tests/Composer/Test/DependencyResolver/SolverTest.php
@@ -16,6 +16,11 @@ use Composer\IO\NullIO;
 use Composer\Repository\ArrayRepository;
 use Composer\Repository\LockArrayRepository;
 use Composer\DependencyResolver\DefaultPolicy;
+use Composer\DependencyResolver\Operation\InstallOperation;
+use Composer\DependencyResolver\Operation\MarkAliasInstalledOperation;
+use Composer\DependencyResolver\Operation\MarkAliasUninstalledOperation;
+use Composer\DependencyResolver\Operation\UninstallOperation;
+use Composer\DependencyResolver\Operation\UpdateOperation;
 use Composer\DependencyResolver\Request;
 use Composer\DependencyResolver\Solver;
 use Composer\DependencyResolver\SolverProblemsException;
@@ -24,15 +29,23 @@ use Composer\Repository\RepositorySet;
 use Composer\Test\TestCase;
 use Composer\Semver\Constraint\MultiConstraint;
 use Composer\Semver\Constraint\MatchAllConstraint;
+use Composer\DependencyResolver\Pool;
 
 class SolverTest extends TestCase
 {
+    /** @var RepositorySet */
     protected $repoSet;
+    /** @var ArrayRepository */
     protected $repo;
+    /** @var LockArrayRepository */
     protected $repoLocked;
+    /** @var Request */
     protected $request;
+    /** @var DefaultPolicy */
     protected $policy;
+    /** @var Solver|null */
     protected $solver;
+    /** @var Pool */
     protected $pool;
 
     public function setUp()
@@ -1046,23 +1059,25 @@ class SolverTest extends TestCase
 
         $result = array();
         foreach ($transaction->getOperations() as $operation) {
-            if ('update' === $operation->getOperationType()) {
+            if ($operation instanceof UpdateOperation) {
                 $result[] = array(
                     'job' => 'update',
                     'from' => $operation->getInitialPackage(),
                     'to' => $operation->getTargetPackage(),
                 );
-            } elseif (in_array($operation->getOperationType(), array('markAliasInstalled', 'markAliasUninstalled'))) {
+            } elseif ($operation instanceof MarkAliasInstalledOperation || $operation instanceof MarkAliasUninstalledOperation) {
                 $result[] = array(
                     'job' => $operation->getOperationType(),
                     'package' => $operation->getPackage(),
                 );
-            } else {
+            } elseif ($operation instanceof UninstallOperation || $operation instanceof InstallOperation) {
                 $job = ('uninstall' === $operation->getOperationType() ? 'remove' : 'install');
                 $result[] = array(
                     'job' => $job,
                     'package' => $operation->getPackage(),
                 );
+            } else {
+                throw new \LogicException('Unexpected operation: '.get_class($operation));
             }
         }
 
diff --git a/tests/Composer/Test/InstalledVersionsTest.php b/tests/Composer/Test/InstalledVersionsTest.php
index 380114a2e..c9e291d3e 100644
--- a/tests/Composer/Test/InstalledVersionsTest.php
+++ b/tests/Composer/Test/InstalledVersionsTest.php
@@ -17,6 +17,9 @@ use Composer\Semver\VersionParser;
 
 class InstalledVersionsTest extends TestCase
 {
+    /**
+     * @var string
+     */
     private $root;
 
     public static function setUpBeforeClass()
diff --git a/tests/Composer/Test/Installer/MetapackageInstallerTest.php b/tests/Composer/Test/Installer/MetapackageInstallerTest.php
index 4ba65991f..012a28a5a 100644
--- a/tests/Composer/Test/Installer/MetapackageInstallerTest.php
+++ b/tests/Composer/Test/Installer/MetapackageInstallerTest.php
@@ -17,8 +17,17 @@ use Composer\Test\TestCase;
 
 class MetapackageInstallerTest extends TestCase
 {
+    /**
+     * @var \Composer\Repository\InstalledRepositoryInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     private $repository;
+    /**
+     * @var MetapackageInstaller
+     */
     private $installer;
+    /**
+     * @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     private $io;
 
     protected function setUp()
diff --git a/tests/Composer/Test/Mock/HttpDownloaderMock.php b/tests/Composer/Test/Mock/HttpDownloaderMock.php
index 1e2774af0..b58a9628a 100644
--- a/tests/Composer/Test/Mock/HttpDownloaderMock.php
+++ b/tests/Composer/Test/Mock/HttpDownloaderMock.php
@@ -18,10 +18,13 @@ use Composer\Downloader\TransportException;
 
 class HttpDownloaderMock extends HttpDownloader
 {
+    /**
+     * @var array<string, string>
+     */
     protected $contentMap;
 
     /**
-     * @param array $contentMap associative array of locations and content
+     * @param array<string, string> $contentMap associative array of locations and content
      */
     public function __construct(array $contentMap)
     {
diff --git a/tests/Composer/Test/Mock/InstallationManagerMock.php b/tests/Composer/Test/Mock/InstallationManagerMock.php
index 46b115771..9e235b917 100644
--- a/tests/Composer/Test/Mock/InstallationManagerMock.php
+++ b/tests/Composer/Test/Mock/InstallationManagerMock.php
@@ -24,9 +24,21 @@ use Composer\DependencyResolver\Operation\MarkAliasUninstalledOperation;
 
 class InstallationManagerMock extends InstallationManager
 {
+    /**
+     * @var PackageInterface[]
+     */
     private $installed = array();
+    /**
+     * @var PackageInterface[][]
+     */
     private $updated = array();
+    /**
+     * @var PackageInterface[]
+     */
     private $uninstalled = array();
+    /**
+     * @var string[]
+     */
     private $trace = array();
 
     public function __construct()
diff --git a/tests/Composer/Test/Mock/ProcessExecutorMock.php b/tests/Composer/Test/Mock/ProcessExecutorMock.php
index 4010e0f4c..3f516eb13 100644
--- a/tests/Composer/Test/Mock/ProcessExecutorMock.php
+++ b/tests/Composer/Test/Mock/ProcessExecutorMock.php
@@ -24,9 +24,21 @@ use React\Promise\Promise;
  */
 class ProcessExecutorMock extends ProcessExecutor
 {
+    /**
+     * @var array<array{cmd: string, return: int, stdout: string, stderr: string, callback: ?callable}>
+     */
     private $expectations = array();
+    /**
+     * @var bool
+     */
     private $strict = false;
+    /**
+     * @var array{return: int, stdout: string, stderr: string}
+     */
     private $defaultHandler = array('return' => 0, 'stdout' => '', 'stderr' => '');
+    /**
+     * @var string[]
+     */
     private $log = array();
 
     /**
@@ -47,7 +59,7 @@ class ProcessExecutorMock extends ProcessExecutor
             return array_merge($default, $expect);
         }, $expectations);
         $this->strict = $strict;
-        $this->defaultHandler = array_merge($default, $defaultHandler);
+        $this->defaultHandler = array_merge($this->defaultHandler, $defaultHandler);
     }
 
     public function assertComplete(TestCase $testCase)
diff --git a/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php b/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
index b8f110937..4742572ea 100644
--- a/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchivableFilesFinderTest.php
@@ -19,8 +19,17 @@ use Symfony\Component\Process\Process;
 
 class ArchivableFilesFinderTest extends TestCase
 {
+    /**
+     * @var string
+     */
     protected $sources;
+    /**
+     * @var ArchivableFilesFinder
+     */
     protected $finder;
+    /**
+     * @var Filesystem
+     */
     protected $fs;
 
     protected function setUp()
diff --git a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
index a9f281975..662a84dd8 100644
--- a/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
+++ b/tests/Composer/Test/Package/Archiver/ArchiveManagerTest.php
@@ -28,6 +28,9 @@ class ArchiveManagerTest extends ArchiverTest
      */
     protected $manager;
 
+    /**
+     * @var string
+     */
     protected $targetDir;
 
     public function setUp()
diff --git a/tests/Composer/Test/Platform/HhvmDetectorTest.php b/tests/Composer/Test/Platform/HhvmDetectorTest.php
index 1387f9aeb..de47672ac 100644
--- a/tests/Composer/Test/Platform/HhvmDetectorTest.php
+++ b/tests/Composer/Test/Platform/HhvmDetectorTest.php
@@ -20,6 +20,9 @@ use Symfony\Component\Process\ExecutableFinder;
 
 class HhvmDetectorTest extends TestCase
 {
+    /**
+     * @var HhvmDetector
+     */
     private $hhvmDetector;
 
     protected function setUp()
diff --git a/tests/Composer/Test/Repository/FilterRepositoryTest.php b/tests/Composer/Test/Repository/FilterRepositoryTest.php
index e3f388da0..bf2953a08 100644
--- a/tests/Composer/Test/Repository/FilterRepositoryTest.php
+++ b/tests/Composer/Test/Repository/FilterRepositoryTest.php
@@ -20,6 +20,9 @@ use Composer\Package\BasePackage;
 
 class FilterRepositoryTest extends TestCase
 {
+    /**
+     * @var ArrayRepository
+     */
     private $arrayRepo;
 
     public function setUp()
diff --git a/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php b/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php
index a6953f834..d43afb7f4 100644
--- a/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/FossilDriverTest.php
@@ -19,7 +19,13 @@ use Composer\Util\Filesystem;
 
 class FossilDriverTest extends TestCase
 {
+    /**
+     * @var string
+     */
     protected $home;
+    /**
+     * @var Config
+     */
     protected $config;
 
     public function setUp()
diff --git a/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
index 2dae0ab21..23c7fb766 100644
--- a/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitBitbucketDriverTest.php
@@ -24,15 +24,15 @@ use Composer\Util\Http\Response;
  */
 class GitBitbucketDriverTest extends TestCase
 {
-    /** @type \Composer\IO\IOInterface|\PHPUnit_Framework_MockObject_MockObject */
+    /** @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject */
     private $io;
-    /** @type \Composer\Config */
+    /** @var Config */
     private $config;
-    /** @type \Composer\Util\HttpDownloader|\PHPUnit_Framework_MockObject_MockObject */
+    /** @var \Composer\Util\HttpDownloader&\PHPUnit\Framework\MockObject\MockObject */
     private $httpDownloader;
-    /** @type string */
+    /** @var string */
     private $home;
-    /** @type string */
+    /** @var string */
     private $originUrl = 'bitbucket.org';
 
     protected function setUp()
diff --git a/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php
index 883231489..e6374a545 100644
--- a/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitLabDriverTest.php
@@ -24,10 +24,25 @@ use Composer\Util\Http\Response;
  */
 class GitLabDriverTest extends TestCase
 {
+    /**
+     * @var string
+     */
     private $home;
+    /**
+     * @var Config
+     */
     private $config;
+    /**
+     * @var \Prophecy\Prophecy\ObjectProphecy
+     */
     private $io;
+    /**
+     * @var \Prophecy\Prophecy\ObjectProphecy
+     */
     private $process;
+    /**
+     * @var \Prophecy\Prophecy\ObjectProphecy
+     */
     private $httpDownloader;
 
     public function setUp()
diff --git a/tests/Composer/Test/Repository/Vcs/HgDriverTest.php b/tests/Composer/Test/Repository/Vcs/HgDriverTest.php
index 11143b476..d7bae8a11 100644
--- a/tests/Composer/Test/Repository/Vcs/HgDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/HgDriverTest.php
@@ -19,11 +19,11 @@ use Composer\Config;
 
 class HgDriverTest extends TestCase
 {
-    /** @type \Composer\IO\IOInterface|\PHPUnit_Framework_MockObject_MockObject */
+    /** @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject */
     private $io;
-    /** @type Config */
+    /** @var Config */
     private $config;
-    /** @type string */
+    /** @var string */
     private $home;
 
     public function setUp()
diff --git a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
index 11f1524d3..520c85e32 100644
--- a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
@@ -24,13 +24,37 @@ use Composer\Test\Mock\ProcessExecutorMock;
  */
 class PerforceDriverTest extends TestCase
 {
+    /**
+     * @var Config
+     */
     protected $config;
+    /**
+     * @var \Composer\IO\IOInterface&\PHPUnit\Framework\MockObject\MockObject
+     */
     protected $io;
+    /**
+     * @var ProcessExecutorMock
+     */
     protected $process;
+    /**
+     * @var \Composer\Util\HttpDownloader&\PHPUnit\Framework\MockObject\MockObject
+     */
     protected $httpDownloader;
+    /**
+     * @var string
+     */
     protected $testPath;
+    /**
+     * @var PerforceDriver
+     */
     protected $driver;
+    /**
+     * @var array<string, string>
+     */
     protected $repoConfig;
+    /**
+     * @var Perforce&\PHPUnit\Framework\MockObject\MockObject
+     */
     protected $perforce;
 
     const TEST_URL = 'TEST_PERFORCE_URL';
@@ -41,7 +65,11 @@ class PerforceDriverTest extends TestCase
     {
         $this->testPath = $this->getUniqueTmpDirectory();
         $this->config = $this->getTestConfig($this->testPath);
-        $this->repoConfig = $this->getTestRepoConfig();
+        $this->repoConfig = array(
+            'url' => self::TEST_URL,
+            'depot' => self::TEST_DEPOT,
+            'branch' => self::TEST_BRANCH,
+        );
         $this->io = $this->getMockIOInterface();
         $this->process = new ProcessExecutorMock;
         $this->httpDownloader = $this->getMockHttpDownloader();
@@ -55,14 +83,6 @@ class PerforceDriverTest extends TestCase
         //cleanup directory under test path
         $fs = new Filesystem;
         $fs->removeDirectory($this->testPath);
-        $this->driver = null;
-        $this->perforce = null;
-        $this->httpDownloader = null;
-        $this->process = null;
-        $this->io = null;
-        $this->repoConfig = null;
-        $this->config = null;
-        $this->testPath = null;
     }
 
     protected function overrideDriverInternalPerforce(Perforce $perforce)
@@ -81,15 +101,6 @@ class PerforceDriverTest extends TestCase
         return $config;
     }
 
-    protected function getTestRepoConfig()
-    {
-        return array(
-            'url' => self::TEST_URL,
-            'depot' => self::TEST_DEPOT,
-            'branch' => self::TEST_BRANCH,
-        );
-    }
-
     protected function getMockIOInterface()
     {
         return $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
diff --git a/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php b/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
index b2699e61b..fe3e896bb 100644
--- a/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
@@ -20,7 +20,13 @@ use Composer\Test\Mock\ProcessExecutorMock;
 
 class SvnDriverTest extends TestCase
 {
+    /**
+     * @var string
+     */
     protected $home;
+    /**
+     * @var Config
+     */
     protected $config;
 
     public function setUp()
diff --git a/tests/Composer/Test/Repository/VcsRepositoryTest.php b/tests/Composer/Test/Repository/VcsRepositoryTest.php
index b1d0e5a83..d517422fb 100644
--- a/tests/Composer/Test/Repository/VcsRepositoryTest.php
+++ b/tests/Composer/Test/Repository/VcsRepositoryTest.php
@@ -26,9 +26,18 @@ use Composer\Config;
  */
 class VcsRepositoryTest extends TestCase
 {
+    /**
+     * @var string
+     */
     private static $composerHome;
+    /**
+     * @var string
+     */
     private static $gitRepo;
-    private $skipped;
+    /**
+     * @var ?string
+     */
+    private $skipped = null;
 
     protected function initialize()
     {
diff --git a/tests/Composer/Test/TestCase.php b/tests/Composer/Test/TestCase.php
index 00a01a838..8a461644d 100644
--- a/tests/Composer/Test/TestCase.php
+++ b/tests/Composer/Test/TestCase.php
@@ -25,7 +25,13 @@ use Composer\Package\BasePackage;
 
 abstract class TestCase extends PolyfillTestCase
 {
+    /**
+     * @var ?VersionParser
+     */
     private static $parser;
+    /**
+     * @var array<string, bool>
+     */
     private static $executableCache = array();
 
     /**
diff --git a/tests/Composer/Test/Util/IniHelperTest.php b/tests/Composer/Test/Util/IniHelperTest.php
index 43048989a..efcdbf9bb 100644
--- a/tests/Composer/Test/Util/IniHelperTest.php
+++ b/tests/Composer/Test/Util/IniHelperTest.php
@@ -21,6 +21,9 @@ use Composer\Test\TestCase;
  */
 class IniHelperTest extends TestCase
 {
+    /**
+     * @var string|false
+     */
     public static $envOriginal;
 
     public function testWithNoIni()