diff --git a/src/Composer/Json/JsonValidationException.php b/src/Composer/Json/JsonValidationException.php
index 2fa5eb489..2d113a802 100644
--- a/src/Composer/Json/JsonValidationException.php
+++ b/src/Composer/Json/JsonValidationException.php
@@ -24,7 +24,7 @@ class JsonValidationException extends Exception
     public function __construct($message, $errors = array(), Exception $previous = null)
     {
         $this->errors = $errors;
-        parent::__construct($message, 0, $previous);
+        parent::__construct((string) $message, 0, $previous);
     }
 
     public function getErrors()
diff --git a/src/Composer/Util/Bitbucket.php b/src/Composer/Util/Bitbucket.php
index 5970aa631..445dbed7e 100644
--- a/src/Composer/Util/Bitbucket.php
+++ b/src/Composer/Util/Bitbucket.php
@@ -151,7 +151,7 @@ class Bitbucket
         $this->io->writeError(sprintf('to create a consumer. It will be stored in "%s" for future use by Composer.', $this->config->getAuthConfigSource()->getName()));
         $this->io->writeError('Ensure you enter a "Callback URL" (http://example.com is fine) or it will not be possible to create an Access Token (this callback url will not be used by composer)');
 
-        $consumerKey = trim($this->io->askAndHideAnswer('Consumer Key (hidden): '));
+        $consumerKey = trim((string) $this->io->askAndHideAnswer('Consumer Key (hidden): '));
 
         if (!$consumerKey) {
             $this->io->writeError('<warning>No consumer key given, aborting.</warning>');
@@ -160,7 +160,7 @@ class Bitbucket
             return false;
         }
 
-        $consumerSecret = trim($this->io->askAndHideAnswer('Consumer Secret (hidden): '));
+        $consumerSecret = trim((string) $this->io->askAndHideAnswer('Consumer Secret (hidden): '));
 
         if (!$consumerSecret) {
             $this->io->writeError('<warning>No consumer secret given, aborting.</warning>');
diff --git a/src/Composer/Util/Perforce.php b/src/Composer/Util/Perforce.php
index 0bde7fb3e..ea2b1152c 100644
--- a/src/Composer/Util/Perforce.php
+++ b/src/Composer/Util/Perforce.php
@@ -160,7 +160,7 @@ class Perforce
 
     public function isStream()
     {
-        return (strcmp($this->p4DepotType, 'stream') === 0);
+        return is_string($this->p4DepotType) && (strcmp($this->p4DepotType, 'stream') === 0);
     }
 
     public function getStream()
@@ -204,11 +204,11 @@ class Perforce
     public function queryP4User()
     {
         $this->getUser();
-        if (strlen($this->p4User) > 0) {
+        if (strlen((string) $this->p4User) > 0) {
             return;
         }
         $this->p4User = $this->getP4variable('P4USER');
-        if (strlen($this->p4User) > 0) {
+        if (strlen((string) $this->p4User) > 0) {
             return;
         }
         $this->p4User = $this->io->ask('Enter P4 User:');
@@ -262,7 +262,7 @@ class Perforce
             return $this->p4Password;
         }
         $password = $this->getP4variable('P4PASSWD');
-        if (strlen($password) <= 0) {
+        if (strlen((string) $password) <= 0) {
             $password = $this->io->askAndHideAnswer('Enter password for Perforce user ' . $this->getUser() . ': ');
         }
         $this->p4Password = $password;
diff --git a/src/Composer/Util/ProcessExecutor.php b/src/Composer/Util/ProcessExecutor.php
index 6b6e84bee..c00e8fd20 100644
--- a/src/Composer/Util/ProcessExecutor.php
+++ b/src/Composer/Util/ProcessExecutor.php
@@ -356,9 +356,9 @@ class ProcessExecutor
      */
     public function splitLines($output)
     {
-        $output = trim($output);
+        $output = trim((string) $output);
 
-        return ((string) $output === '') ? array() : preg_split('{\r?\n}', $output);
+        return $output === '' ? array() : preg_split('{\r?\n}', $output);
     }
 
     /**
diff --git a/tests/Composer/Test/Downloader/FileDownloaderTest.php b/tests/Composer/Test/Downloader/FileDownloaderTest.php
index ead8bc1c1..036410407 100644
--- a/tests/Composer/Test/Downloader/FileDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FileDownloaderTest.php
@@ -18,6 +18,7 @@ use Composer\EventDispatcher\EventDispatcher;
 use Composer\Plugin\PluginEvents;
 use Composer\Plugin\PreFileDownloadEvent;
 use Composer\Test\TestCase;
+use Composer\Test\Mock\ProcessExecutorMock;
 use Composer\Util\Filesystem;
 use Composer\Util\Http\Response;
 use Composer\Util\Loop;
@@ -194,7 +195,7 @@ class FileDownloaderTest extends TestCase
         $dispatcher = new EventDispatcher(
             $composerMock,
             $this->getMockBuilder('Composer\IO\IOInterface')->getMock(),
-            $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock()
+            new ProcessExecutorMock
         );
         $dispatcher->addListener(PluginEvents::PRE_FILE_DOWNLOAD, function (PreFileDownloadEvent $event) use ($expectedUrl) {
             $event->setProcessedUrl($expectedUrl);
@@ -288,7 +289,7 @@ class FileDownloaderTest extends TestCase
         $dispatcher = new EventDispatcher(
             $composerMock,
             $this->getMockBuilder('Composer\IO\IOInterface')->getMock(),
-            $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock()
+            new ProcessExecutorMock
         );
         $dispatcher->addListener(PluginEvents::PRE_FILE_DOWNLOAD, function (PreFileDownloadEvent $event) use ($customCacheKey) {
             $event->setCustomCacheKey($customCacheKey);
diff --git a/tests/Composer/Test/Downloader/FossilDownloaderTest.php b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
index 33920da27..69a810977 100644
--- a/tests/Composer/Test/Downloader/FossilDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/FossilDownloaderTest.php
@@ -16,6 +16,7 @@ use Composer\Downloader\FossilDownloader;
 use Composer\Test\TestCase;
 use Composer\Util\Filesystem;
 use Composer\Util\Platform;
+use Composer\Test\Mock\ProcessExecutorMock;
 
 class FossilDownloaderTest extends TestCase
 {
@@ -39,7 +40,7 @@ class FossilDownloaderTest extends TestCase
     {
         $io = $io ?: $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $config = $config ?: $this->getMockBuilder('Composer\Config')->getMock();
-        $executor = $executor ?: $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
+        $executor = $executor ?: new ProcessExecutorMock;
         $filesystem = $filesystem ?: $this->getMockBuilder('Composer\Util\Filesystem')->getMock();
 
         return new FossilDownloader($io, $config, $executor, $filesystem);
@@ -67,28 +68,18 @@ class FossilDownloaderTest extends TestCase
         $packageMock->expects($this->once())
             ->method('getSourceUrls')
             ->will($this->returnValue(array('http://fossil.kd2.org/kd2fw/')));
-        $processExecutor = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
 
-        $expectedFossilCommand = $this->getCmd('fossil clone -- \'http://fossil.kd2.org/kd2fw/\' \'repo.fossil\'');
-        $processExecutor->expects($this->at(0))
-            ->method('execute')
-            ->with($this->equalTo($expectedFossilCommand))
-            ->will($this->returnValue(0));
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            $this->getCmd('fossil clone -- \'http://fossil.kd2.org/kd2fw/\' \'repo.fossil\''),
+            $this->getCmd('fossil open --nested -- \'repo.fossil\''),
+            $this->getCmd('fossil update -- \'trunk\''),
+        ), true);
 
-        $expectedFossilCommand = $this->getCmd('fossil open --nested -- \'repo.fossil\'');
-        $processExecutor->expects($this->at(1))
-            ->method('execute')
-            ->with($this->equalTo($expectedFossilCommand))
-            ->will($this->returnValue(0));
-
-        $expectedFossilCommand = $this->getCmd('fossil update -- \'trunk\'');
-        $processExecutor->expects($this->at(2))
-            ->method('execute')
-            ->with($this->equalTo($expectedFossilCommand))
-            ->will($this->returnValue(0));
-
-        $downloader = $this->getDownloaderMock(null, null, $processExecutor);
+        $downloader = $this->getDownloaderMock(null, null, $process);
         $downloader->install($packageMock, 'repo');
+
+        $process->assertComplete($this);
     }
 
     public function testUpdateforPackageWithoutSourceReference()
@@ -126,46 +117,46 @@ class FossilDownloaderTest extends TestCase
         $packageMock->expects($this->any())
             ->method('getVersion')
             ->will($this->returnValue('1.0.0.0'));
-        $processExecutor = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
 
-        $expectedFossilCommand = $this->getCmd("fossil changes");
-        $processExecutor->expects($this->at(0))
-            ->method('execute')
-            ->with($this->equalTo($expectedFossilCommand))
-            ->will($this->returnCallback(function ($cmd, &$output, $path) {
-                $output = '';
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            $this->getCmd("fossil changes"),
+            $this->getCmd("fossil pull && fossil up 'trunk'"),
+        ), true);
 
-                return 0;
-            }));
-        $expectedFossilCommand = $this->getCmd("fossil pull && fossil up 'trunk'");
-        $processExecutor->expects($this->at(1))
-            ->method('execute')
-            ->with($this->equalTo($expectedFossilCommand))
-            ->will($this->returnValue(0));
-
-        $downloader = $this->getDownloaderMock(null, null, $processExecutor);
+        $downloader = $this->getDownloaderMock(null, null, $process);
         $downloader->prepare('update', $packageMock, $this->workingDir, $packageMock);
         $downloader->update($packageMock, $packageMock, $this->workingDir);
         $downloader->cleanup('update', $packageMock, $this->workingDir, $packageMock);
+
+        $process->assertComplete($this);
     }
 
     public function testRemove()
     {
-        $expectedResetCommand = $this->getCmd('cd \'composerPath\' && fossil status');
+        // Ensure file exists
+        $file = $this->workingDir . '/.fslckout';
+        touch($file);
 
         $packageMock = $this->getMockBuilder('Composer\Package\PackageInterface')->getMock();
-        $processExecutor = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-        $processExecutor->expects($this->any())
-            ->method('execute')
-            ->with($this->equalTo($expectedResetCommand));
+
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            $this->getCmd('fossil changes'),
+        ), true);
+
         $filesystem = $this->getMockBuilder('Composer\Util\Filesystem')->getMock();
         $filesystem->expects($this->once())
             ->method('removeDirectoryAsync')
-            ->with($this->equalTo('composerPath'))
+            ->with($this->equalTo($this->workingDir))
             ->will($this->returnValue(\React\Promise\resolve(true)));
 
-        $downloader = $this->getDownloaderMock(null, null, $processExecutor, $filesystem);
-        $downloader->remove($packageMock, 'composerPath');
+        $downloader = $this->getDownloaderMock(null, null, $process, $filesystem);
+        $downloader->prepare('uninstall', $packageMock, $this->workingDir);
+        $downloader->remove($packageMock, $this->workingDir);
+        $downloader->cleanup('uninstall', $packageMock, $this->workingDir);
+
+        $process->assertComplete($this);
     }
 
     public function testGetInstallationSource()
diff --git a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
index 370fc9d31..cd47d8ecf 100644
--- a/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
+++ b/tests/Composer/Test/Downloader/PerforceDownloaderTest.php
@@ -19,6 +19,7 @@ use Composer\IO\IOInterface;
 use Composer\Test\TestCase;
 use Composer\Factory;
 use Composer\Util\Filesystem;
+use Composer\Test\Mock\ProcessExecutorMock;
 
 /**
  * @author Matt Whittom <Matt.Whittom@veteransunited.com>
@@ -41,7 +42,7 @@ class PerforceDownloaderTest extends TestCase
         $this->repoConfig = $this->getRepoConfig();
         $this->config = $this->getConfig();
         $this->io = $this->getMockIoInterface();
-        $this->processExecutor = $this->getMockProcessExecutor();
+        $this->processExecutor = new ProcessExecutorMock;
         $this->repository = $this->getMockRepository($this->repoConfig, $this->io, $this->config);
         $this->package = $this->getMockPackageInterface($this->repository);
         $this->downloader = new PerforceDownloader($this->io, $this->config, $this->processExecutor);
@@ -61,11 +62,6 @@ class PerforceDownloaderTest extends TestCase
         }
     }
 
-    protected function getMockProcessExecutor()
-    {
-        return $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-    }
-
     protected function getConfig()
     {
         $config = new Config();
diff --git a/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php b/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
index bbf3e6b98..400f4dec9 100644
--- a/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
+++ b/tests/Composer/Test/EventDispatcher/EventDispatcherTest.php
@@ -22,6 +22,7 @@ use Composer\IO\BufferIO;
 use Composer\Script\ScriptEvents;
 use Composer\Script\Event as ScriptEvent;
 use Composer\Util\ProcessExecutor;
+use Composer\Test\Mock\ProcessExecutorMock;
 use Symfony\Component\Console\Output\OutputInterface;
 
 class EventDispatcherTest extends TestCase
@@ -56,7 +57,11 @@ class EventDispatcherTest extends TestCase
      */
     public function testDispatcherCanExecuteSingleCommandLineScript($command)
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            $command,
+        ), true);
+
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
             ->setConstructorArgs(array(
                 $this->createComposerInstance(),
@@ -71,12 +76,9 @@ class EventDispatcherTest extends TestCase
             ->method('getListeners')
             ->will($this->returnValue($listener));
 
-        $process->expects($this->once())
-            ->method('execute')
-            ->with($command)
-            ->will($this->returnValue(0));
-
         $dispatcher->dispatchScript(ScriptEvents::POST_INSTALL_CMD, false);
+
+        $process->assertComplete($this);
     }
 
     /**
@@ -104,7 +106,7 @@ class EventDispatcherTest extends TestCase
         $dispatcher = new EventDispatcher(
             $composer,
             $this->getMockBuilder('Composer\IO\IOInterface')->getMock(),
-            $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock()
+            new ProcessExecutorMock
         );
 
         $event = $this->getMockBuilder('Composer\Script\Event')
@@ -179,7 +181,7 @@ class EventDispatcherTest extends TestCase
         $dispatcher = new EventDispatcher(
             $composer,
             $io = new BufferIO('', OutputInterface::VERBOSITY_VERBOSE),
-            $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock()
+            new ProcessExecutorMock
         );
 
         $listener = array($this, 'someMethod');
@@ -214,7 +216,12 @@ class EventDispatcherTest extends TestCase
 
     public function testDispatcherCanExecuteCliAndPhpInSameEventScriptStack()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            'echo -n foo',
+            'echo -n bar',
+        ), true);
+
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
             ->setConstructorArgs(array(
                 $this->createComposerInstance(),
@@ -226,10 +233,6 @@ class EventDispatcherTest extends TestCase
             ))
             ->getMock();
 
-        $process->expects($this->exactly(2))
-            ->method('execute')
-            ->will($this->returnValue(0));
-
         $listeners = array(
             'echo -n foo',
             'Composer\\Test\\EventDispatcher\\EventDispatcherTest::someMethod',
@@ -246,16 +249,17 @@ class EventDispatcherTest extends TestCase
             '> post-install-cmd: Composer\Test\EventDispatcher\EventDispatcherTest::someMethod'.PHP_EOL.
             '> post-install-cmd: echo -n bar'.PHP_EOL;
         $this->assertEquals($expected, $io->getOutput());
+
+        $process->assertComplete($this);
     }
 
     public function testDispatcherCanPutEnv()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
             ->setConstructorArgs(array(
                 $this->createComposerInstance(),
                 $io = new BufferIO('', OutputInterface::VERBOSITY_VERBOSE),
-                $process,
+                new ProcessExecutorMock,
             ))
             ->setMethods(array(
                 'getListeners',
@@ -285,11 +289,10 @@ class EventDispatcherTest extends TestCase
         chdir(__DIR__);
         putenv('COMPOSER_BIN_DIR=' . __DIR__ . sprintf('%svendor%sbin', DIRECTORY_SEPARATOR, DIRECTORY_SEPARATOR));
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')->setConstructorArgs(array(
                 $this->createComposerInstance(),
                 $io = new BufferIO('', OutputInterface::VERBOSITY_VERBOSE),
-                $process,
+                new ProcessExecutorMock,
             ))->setMethods(array(
                 'getListeners',
             ))->getMock();
@@ -342,7 +345,13 @@ class EventDispatcherTest extends TestCase
 
     public function testDispatcherCanExecuteComposerScriptGroups()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            'echo -n foo',
+            'echo -n baz',
+            'echo -n bar',
+        ), true);
+
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
             ->setConstructorArgs(array(
                 $composer = $this->createComposerInstance(),
@@ -354,10 +363,6 @@ class EventDispatcherTest extends TestCase
             ))
             ->getMock();
 
-        $process->expects($this->exactly(3))
-            ->method('execute')
-            ->will($this->returnValue(0));
-
         $dispatcher->expects($this->atLeastOnce())
             ->method('getListeners')
             ->will($this->returnCallback(function (Event $event) {
@@ -383,11 +388,17 @@ class EventDispatcherTest extends TestCase
             '> subgroup: echo -n baz'.PHP_EOL.
             '> group: echo -n bar'.PHP_EOL;
         $this->assertEquals($expected, $io->getOutput());
+
+        $process->assertComplete($this);
     }
 
     public function testRecursionInScriptsNames()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            'echo Hello '.ProcessExecutor::escape('World'),
+        ), true);
+
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
             ->setConstructorArgs(array(
                 $composer = $this->createComposerInstance(),
@@ -399,10 +410,6 @@ class EventDispatcherTest extends TestCase
             ))
             ->getMock();
 
-        $process->expects($this->exactly(1))
-            ->method('execute')
-            ->will($this->returnValue(0));
-
         $dispatcher->expects($this->atLeastOnce())
             ->method('getListeners')
             ->will($this->returnCallback(function (Event $event) {
@@ -422,18 +429,19 @@ class EventDispatcherTest extends TestCase
             "> hello: echo Hello " .escapeshellarg('World').PHP_EOL;
 
         $this->assertEquals($expected, $io->getOutput());
+
+        $process->assertComplete($this);
     }
 
     public function testDispatcherDetectInfiniteRecursion()
     {
         $this->setExpectedException('RuntimeException');
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
         ->setConstructorArgs(array(
             $composer = $this->createComposerInstance(),
             $io = $this->getMockBuilder('Composer\IO\IOInterface')->getMock(),
-            $process,
+            new ProcessExecutorMock,
         ))
         ->setMethods(array(
             'getListeners',
@@ -549,12 +557,11 @@ class EventDispatcherTest extends TestCase
 
     public function testDispatcherInstallerEvents()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
         $dispatcher = $this->getMockBuilder('Composer\EventDispatcher\EventDispatcher')
             ->setConstructorArgs(array(
                     $this->createComposerInstance(),
                     $this->getMockBuilder('Composer\IO\IOInterface')->getMock(),
-                    $process,
+                    new ProcessExecutorMock,
                 ))
             ->setMethods(array('getListeners'))
             ->getMock();
diff --git a/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php b/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
index 880b6f766..d83208632 100644
--- a/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
+++ b/tests/Composer/Test/Package/Loader/RootPackageLoaderTest.php
@@ -19,13 +19,14 @@ use Composer\Package\RootPackage;
 use Composer\Package\Version\VersionGuesser;
 use Composer\Semver\VersionParser;
 use Composer\Test\TestCase;
+use Composer\Test\Mock\ProcessExecutorMock;
 use Prophecy\Argument;
 
 class RootPackageLoaderTest extends TestCase
 {
     protected function loadPackage($data)
     {
-        $manager = $this->getMockBuilder('\\Composer\\Repository\\RepositoryManager')
+        $manager = $this->getMockBuilder('Composer\\Repository\\RepositoryManager')
             ->disableOriginalConstructor()
             ->getMock();
 
@@ -67,38 +68,28 @@ class RootPackageLoaderTest extends TestCase
 
     public function testNoVersionIsVisibleInPrettyVersion()
     {
-        $manager = $this->getMockBuilder('\\Composer\\Repository\\RepositoryManager')
+        $manager = $this->getMockBuilder('Composer\\Repository\\RepositoryManager')
             ->disableOriginalConstructor()
             ->getMock()
         ;
 
-        $executor = $this->getMockBuilder('\\Composer\\Util\\ProcessExecutor')
-            ->setMethods(array('execute'))
-            ->disableArgumentCloning()
-            ->disableOriginalConstructor()
-            ->getMock()
-        ;
-
-        $executor
-            ->expects($this->any())
-            ->method('execute')
-            ->willReturn(null)
-        ;
-
         $config = new Config;
         $config->merge(array('repositories' => array('packagist' => false)));
-        $loader = new RootPackageLoader($manager, $config, null, new VersionGuesser($config, $executor, new VersionParser()));
+        $loader = new RootPackageLoader($manager, $config, null, new VersionGuesser($config, $process = new ProcessExecutorMock, new VersionParser()));
+        $process->expects(array(), false, array('return' => 1));
+
         $package = $loader->load(array());
 
         $this->assertEquals("1.0.0.0", $package->getVersion());
         $this->assertEquals(RootPackage::DEFAULT_PRETTY_VERSION, $package->getPrettyVersion());
+
     }
 
     public function testPrettyVersionForRootPackageInVersionBranch()
     {
         // see #6845
-        $manager = $this->prophesize('\\Composer\\Repository\\RepositoryManager');
-        $versionGuesser = $this->prophesize('\\Composer\\Package\\Version\\VersionGuesser');
+        $manager = $this->prophesize('Composer\\Repository\\RepositoryManager');
+        $versionGuesser = $this->prophesize('Composer\\Package\\Version\\VersionGuesser');
         $versionGuesser->guessVersion(Argument::cetera())
             ->willReturn(array(
                 'name' => 'A',
@@ -120,48 +111,28 @@ class RootPackageLoaderTest extends TestCase
             $this->markTestSkipped('proc_open() is not available');
         }
 
-        $manager = $this->getMockBuilder('\\Composer\\Repository\\RepositoryManager')
+        $manager = $this->getMockBuilder('Composer\\Repository\\RepositoryManager')
             ->disableOriginalConstructor()
             ->getMock()
         ;
 
-        $executor = $this->getMockBuilder('\\Composer\\Util\\ProcessExecutor')
-            ->setMethods(array('execute'))
-            ->disableArgumentCloning()
-            ->disableOriginalConstructor()
-            ->getMock()
-        ;
-
-        $self = $this;
-
-        $executor
-            ->expects($this->at(0))
-            ->method('execute')
-            ->willReturnCallback(function ($command, &$output) use ($self) {
-                $self->assertEquals('git branch -a --no-color --no-abbrev -v', $command);
-                $output = "* latest-production 38137d2f6c70e775e137b2d8a7a7d3eaebf7c7e5 Commit message\n  master 4f6ed96b0bc363d2aa4404c3412de1c011f67c66 Commit message\n";
-
-                return 0;
-            })
-        ;
-
-        $executor
-            ->expects($this->at(1))
-            ->method('execute')
-            ->willReturnCallback(function ($command, &$output) use ($self) {
-                $self->assertEquals('git rev-list master..latest-production', $command);
-                $output = "";
-
-                return 0;
-            })
-        ;
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            array(
+                'cmd' => 'git branch -a --no-color --no-abbrev -v',
+                'stdout' => "* latest-production 38137d2f6c70e775e137b2d8a7a7d3eaebf7c7e5 Commit message\n  master 4f6ed96b0bc363d2aa4404c3412de1c011f67c66 Commit message\n",
+            ),
+            'git rev-list master..latest-production',
+        ), true);
 
         $config = new Config;
         $config->merge(array('repositories' => array('packagist' => false)));
-        $loader = new RootPackageLoader($manager, $config, null, new VersionGuesser($config, $executor, new VersionParser()));
+        $loader = new RootPackageLoader($manager, $config, null, new VersionGuesser($config, $process, new VersionParser()));
         $package = $loader->load(array('require' => array('foo/bar' => 'self.version')));
 
         $this->assertEquals("dev-master", $package->getPrettyVersion());
+
+        $process->assertComplete($this);
     }
 
     public function testNonFeatureBranchPrettyVersion()
@@ -170,36 +141,26 @@ class RootPackageLoaderTest extends TestCase
             $this->markTestSkipped('proc_open() is not available');
         }
 
-        $manager = $this->getMockBuilder('\\Composer\\Repository\\RepositoryManager')
+        $manager = $this->getMockBuilder('Composer\\Repository\\RepositoryManager')
             ->disableOriginalConstructor()
             ->getMock()
         ;
 
-        $executor = $this->getMockBuilder('\\Composer\\Util\\ProcessExecutor')
-            ->setMethods(array('execute'))
-            ->disableArgumentCloning()
-            ->disableOriginalConstructor()
-            ->getMock()
-        ;
-
-        $self = $this;
-
-        $executor
-            ->expects($this->at(0))
-            ->method('execute')
-            ->willReturnCallback(function ($command, &$output) use ($self) {
-                $self->assertEquals('git branch -a --no-color --no-abbrev -v', $command);
-                $output = "* latest-production 38137d2f6c70e775e137b2d8a7a7d3eaebf7c7e5 Commit message\n  master 4f6ed96b0bc363d2aa4404c3412de1c011f67c66 Commit message\n";
-
-                return 0;
-            })
-        ;
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            array(
+                'cmd' => 'git branch -a --no-color --no-abbrev -v',
+                'stdout' => "* latest-production 38137d2f6c70e775e137b2d8a7a7d3eaebf7c7e5 Commit message\n  master 4f6ed96b0bc363d2aa4404c3412de1c011f67c66 Commit message\n"
+            ),
+        ), true);
 
         $config = new Config;
         $config->merge(array('repositories' => array('packagist' => false)));
-        $loader = new RootPackageLoader($manager, $config, null, new VersionGuesser($config, $executor, new VersionParser()));
+        $loader = new RootPackageLoader($manager, $config, null, new VersionGuesser($config, $process, new VersionParser()));
         $package = $loader->load(array('require' => array('foo/bar' => 'self.version'), "non-feature-branches" => array("latest-.*")));
 
         $this->assertEquals("dev-latest-production", $package->getPrettyVersion());
+
+        $process->assertComplete($this);
     }
 }
diff --git a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
index 7c2727c20..38dd7bc34 100644
--- a/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/GitHubDriverTest.php
@@ -17,7 +17,10 @@ use Composer\Repository\Vcs\GitHubDriver;
 use Composer\Test\TestCase;
 use Composer\Util\Filesystem;
 use Composer\Util\Http\Response;
+use Composer\Test\Mock\ProcessExecutorMock;
 use Composer\Config;
+use Composer\Util\ProcessExecutor;
+use Symfony\Component\Process\Process;
 
 class GitHubDriverTest extends TestCase
 {
@@ -58,10 +61,8 @@ class GitHubDriverTest extends TestCase
             ->setConstructorArgs(array($io, $this->config))
             ->getMock();
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-        $process->expects($this->any())
-            ->method('execute')
-            ->will($this->returnValue(1));
+        $process = new ProcessExecutorMock;
+        $process->expects(array(), false, array('return' => 1));
 
         $httpDownloader->expects($this->at(0))
             ->method('get')
@@ -139,11 +140,7 @@ class GitHubDriverTest extends TestCase
         );
         $repoUrl = 'https://github.com/composer/packagist.git';
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')
-            ->disableOriginalConstructor()
-            ->getMock();
-
-        $gitHubDriver = new GitHubDriver($repoConfig, $io, $this->config, $httpDownloader, $process);
+        $gitHubDriver = new GitHubDriver($repoConfig, $io, $this->config, $httpDownloader, new ProcessExecutorMock);
         $gitHubDriver->initialize();
         $this->setAttribute($gitHubDriver, 'tags', array($identifier => $sha));
 
@@ -201,11 +198,7 @@ class GitHubDriverTest extends TestCase
         );
         $repoUrl = 'https://github.com/composer/packagist.git';
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')
-            ->disableOriginalConstructor()
-            ->getMock();
-
-        $gitHubDriver = new GitHubDriver($repoConfig, $io, $this->config, $httpDownloader, $process);
+        $gitHubDriver = new GitHubDriver($repoConfig, $io, $this->config, $httpDownloader, new ProcessExecutorMock);
         $gitHubDriver->initialize();
         $this->setAttribute($gitHubDriver, 'tags', array($identifier => $sha));
 
@@ -239,10 +232,6 @@ class GitHubDriverTest extends TestCase
             ->method('isInteractive')
             ->will($this->returnValue(true));
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')
-            ->disableOriginalConstructor()
-            ->getMock();
-
         $httpDownloader = $this->getMockBuilder('Composer\Util\HttpDownloader')
             ->setConstructorArgs(array($io, $this->config))
             ->getMock();
@@ -271,7 +260,7 @@ class GitHubDriverTest extends TestCase
             'url' => $repoUrl,
         );
 
-        $gitHubDriver = new GitHubDriver($repoConfig, $io, $this->config, $httpDownloader, $process);
+        $gitHubDriver = new GitHubDriver($repoConfig, $io, $this->config, $httpDownloader, new ProcessExecutorMock);
         $gitHubDriver->initialize();
         $this->setAttribute($gitHubDriver, 'tags', array($identifier => $sha));
 
@@ -288,10 +277,6 @@ class GitHubDriverTest extends TestCase
         $identifier = 'v0.0.0';
         $sha = 'SOMESHA';
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')
-            ->disableOriginalConstructor()
-            ->getMock();
-
         $io = $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $io->expects($this->any())
             ->method('isInteractive')
@@ -310,39 +295,23 @@ class GitHubDriverTest extends TestCase
         $fs = new Filesystem();
         $fs->removeDirectory(sys_get_temp_dir() . '/composer-test');
 
-        $process->expects($this->at(0))
-            ->method('execute')
-            ->with($this->equalTo('git config github.accesstoken'))
-            ->will($this->returnValue(1));
-
-        $process->expects($this->at(1))
-            ->method('execute')
-            ->with($this->stringContains($repoSshUrl))
-            ->will($this->returnValue(0));
-
-        $process->expects($this->at(2))
-            ->method('execute')
-            ->with($this->stringContains('git show-ref --tags'));
-
-        $process->expects($this->at(3))
-            ->method('splitLines')
-            ->will($this->returnValue(array($sha.' refs/tags/'.$identifier)));
-
-        $process->expects($this->at(4))
-            ->method('execute')
-            ->with($this->stringContains('git branch --no-color --no-abbrev -v'));
-
-        $process->expects($this->at(5))
-            ->method('splitLines')
-            ->will($this->returnValue(array('  test_master     edf93f1fccaebd8764383dc12016d0a1a9672d89 Fix test & behavior')));
-
-        $process->expects($this->at(6))
-            ->method('execute')
-            ->with($this->stringContains('git branch --no-color'));
-
-        $process->expects($this->at(7))
-            ->method('splitLines')
-            ->will($this->returnValue(array('* test_master')));
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            array('cmd' => 'git config github.accesstoken', 'return' => 1),
+            'git clone --mirror -- '.ProcessExecutor::escape($repoSshUrl).' '.ProcessExecutor::escape($this->config->get('cache-vcs-dir').'/git-github.com-composer-packagist.git/'),
+            array(
+                'cmd' => 'git show-ref --tags --dereference',
+                'stdout' => $sha.' refs/tags/'.$identifier,
+            ),
+            array(
+                'cmd' => 'git branch --no-color --no-abbrev -v',
+                'stdout' => '  test_master     edf93f1fccaebd8764383dc12016d0a1a9672d89 Fix test & behavior',
+            ),
+            array(
+                'cmd' => 'git branch --no-color',
+                'stdout' => '* test_master',
+            ),
+        ), true);
 
         $repoConfig = array(
             'url' => $repoUrl,
@@ -367,6 +336,8 @@ class GitHubDriverTest extends TestCase
         $this->assertEquals('git', $source['type']);
         $this->assertEquals($repoSshUrl, $source['url']);
         $this->assertEquals($sha, $source['reference']);
+
+        $process->assertComplete($this);
     }
 
     protected function setAttribute($object, $attribute, $value)
diff --git a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
index 1c44e82dd..11f1524d3 100644
--- a/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/PerforceDriverTest.php
@@ -17,6 +17,7 @@ use Composer\Test\TestCase;
 use Composer\Util\Filesystem;
 use Composer\Config;
 use Composer\Util\Perforce;
+use Composer\Test\Mock\ProcessExecutorMock;
 
 /**
  * @author Matt Whittom <Matt.Whittom@veteransunited.com>
@@ -42,7 +43,7 @@ class PerforceDriverTest extends TestCase
         $this->config = $this->getTestConfig($this->testPath);
         $this->repoConfig = $this->getTestRepoConfig();
         $this->io = $this->getMockIOInterface();
-        $this->process = $this->getMockProcessExecutor();
+        $this->process = new ProcessExecutorMock;
         $this->httpDownloader = $this->getMockHttpDownloader();
         $this->perforce = $this->getMockPerforce();
         $this->driver = new PerforceDriver($this->repoConfig, $this->io, $this->config, $this->httpDownloader, $this->process);
@@ -94,11 +95,6 @@ class PerforceDriverTest extends TestCase
         return $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
     }
 
-    protected function getMockProcessExecutor()
-    {
-        return $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-    }
-
     protected function getMockHttpDownloader()
     {
         return $this->getMockBuilder('Composer\Util\HttpDownloader')->disableOriginalConstructor()->getMock();
diff --git a/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php b/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
index 9c61c3105..b2699e61b 100644
--- a/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
+++ b/tests/Composer/Test/Repository/Vcs/SvnDriverTest.php
@@ -16,6 +16,7 @@ use Composer\Repository\Vcs\SvnDriver;
 use Composer\Config;
 use Composer\Test\TestCase;
 use Composer\Util\Filesystem;
+use Composer\Test\Mock\ProcessExecutorMock;
 
 class SvnDriverTest extends TestCase
 {
@@ -50,16 +51,11 @@ class SvnDriverTest extends TestCase
         $output .= " authorization failed: Could not authenticate to server:";
         $output .= " rejected Basic challenge (https://corp.svn.local/)";
 
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-        $process->expects($this->at(1))
-            ->method('execute')
-            ->will($this->returnValue(1));
-        $process->expects($this->exactly(7))
-            ->method('getErrorOutput')
-            ->will($this->returnValue($output));
-        $process->expects($this->at(2))
-            ->method('execute')
-            ->will($this->returnValue(0));
+        $process = new ProcessExecutorMock;
+        $process->expects(array(
+            'svn --version',
+            array('cmd' => '', 'return' => 1, 'stderr' => $output),
+        ), true);
 
         $repoConfig = array(
             'url' => 'https://till:secret@corp.svn.local/repo',
@@ -67,6 +63,8 @@ class SvnDriverTest extends TestCase
 
         $svn = new SvnDriver($repoConfig, $console, $this->config, $httpDownloader, $process);
         $svn->initialize();
+
+        $process->assertComplete($this);
     }
 
     public static function supportProvider()
diff --git a/tests/Composer/Test/Util/BitbucketTest.php b/tests/Composer/Test/Util/BitbucketTest.php
index 3262c2fe8..3182ac014 100644
--- a/tests/Composer/Test/Util/BitbucketTest.php
+++ b/tests/Composer/Test/Util/BitbucketTest.php
@@ -15,6 +15,7 @@ namespace Composer\Test\Util;
 use Composer\Util\Bitbucket;
 use Composer\Util\Http\Response;
 use Composer\Test\TestCase;
+use Composer\Test\Mock\ProcessExecutorMock;
 
 /**
  * @author Paul Wenke <wenke.paul@gmail.com>
@@ -456,10 +457,8 @@ class BitbucketTest extends TestCase
 
     public function testAuthorizeOAuthWithoutAvailableGitConfigToken()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-        $process->expects($this->once())
-            ->method('execute')
-            ->willReturn(-1);
+        $process = new ProcessExecutorMock;
+        $process->expects(array(), false, array('return' => -1));
 
         $bitbucket = new Bitbucket($this->io, $this->config, $process, $this->httpDownloader, $this->time);
 
@@ -468,10 +467,7 @@ class BitbucketTest extends TestCase
 
     public function testAuthorizeOAuthWithAvailableGitConfigToken()
     {
-        $process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->getMock();
-        $process->expects($this->once())
-            ->method('execute')
-            ->willReturn(0);
+        $process = new ProcessExecutorMock;
 
         $bitbucket = new Bitbucket($this->io, $this->config, $process, $this->httpDownloader, $this->time);
 
diff --git a/tests/Composer/Test/Util/GitLabTest.php b/tests/Composer/Test/Util/GitLabTest.php
index 7c671afc0..e5ba33db6 100644
--- a/tests/Composer/Test/Util/GitLabTest.php
+++ b/tests/Composer/Test/Util/GitLabTest.php
@@ -93,8 +93,9 @@ class GitLabTest extends TestCase
         $httpDownloader
             ->expects($this->exactly(5))
             ->method('get')
-            ->will($this->throwException(new TransportException('', 401)))
+            ->will($this->throwException($e = new TransportException('', 401)))
         ;
+        $e->setResponse('{}');
 
         $config = $this->getConfigMock();
         $config
diff --git a/tests/Composer/Test/Util/GitTest.php b/tests/Composer/Test/Util/GitTest.php
index 4fbc1826a..f1df7c2f7 100644
--- a/tests/Composer/Test/Util/GitTest.php
+++ b/tests/Composer/Test/Util/GitTest.php
@@ -16,7 +16,7 @@ use Composer\Config;
 use Composer\IO\IOInterface;
 use Composer\Util\Filesystem;
 use Composer\Util\Git;
-use Composer\Util\ProcessExecutor;
+use Composer\Test\Mock\ProcessExecutorMock;
 use Composer\Test\TestCase;
 
 class GitTest extends TestCase
@@ -27,7 +27,7 @@ class GitTest extends TestCase
     private $io;
     /** @var Config&\PHPUnit\Framework\MockObject\MockObject */
     private $config;
-    /** @var ProcessExecutor&\PHPUnit\Framework\MockObject\MockObject */
+    /** @var ProcessExecutorMock */
     private $process;
     /** @var Filesystem&\PHPUnit\Framework\MockObject\MockObject */
     private $fs;
@@ -36,7 +36,7 @@ class GitTest extends TestCase
     {
         $this->io = $this->getMockBuilder('Composer\IO\IOInterface')->getMock();
         $this->config = $this->getMockBuilder('Composer\Config')->disableOriginalConstructor()->getMock();
-        $this->process = $this->getMockBuilder('Composer\Util\ProcessExecutor')->disableOriginalConstructor()->getMock();
+        $this->process = new ProcessExecutorMock;
         $this->fs = $this->getMockBuilder('Composer\Util\Filesystem')->disableOriginalConstructor()->getMock();
         $this->git = new Git($this->io, $this->config, $this->process, $this->fs);
     }
@@ -55,13 +55,11 @@ class GitTest extends TestCase
 
         $this->mockConfig($protocol);
 
-        $this->process
-            ->expects($this->once())
-            ->method('execute')
-            ->with($this->equalTo('git command'))
-            ->willReturn(0);
+        $this->process->expects(array('git command'), true);
 
         $this->git->runCommand($commandCallable, 'https://github.com/acme/repo', null, true);
+
+        $this->process->assertComplete($this);
     }
 
     public function publicGithubNoCredentialsProvider()
@@ -85,20 +83,21 @@ class GitTest extends TestCase
 
         $this->mockConfig('https');
 
-        $this->process
-            ->method('execute')
-            ->willReturnMap(array(
-                array('git command', null, null, 1),
-                array('git --version', null, null, 0),
-            ));
+
+        $this->process->expects(array(
+            array('cmd' => 'git command', 'return' => 1),
+            array('cmd' => 'git --version', 'return' => 0),
+        ), true);
 
         $this->git->runCommand($commandCallable, 'https://github.com/acme/repo', null, true);
+
+        $this->process->assertComplete($this);
     }
 
     /**
      * @dataProvider privateGithubWithCredentialsProvider
      */
-    public function testRunCommandPrivateGitHubRepositoryNotInitialCloneNotInteractiveWithAuthentication($gitUrl, $protocol, $gitHubToken, $expectedUrl)
+    public function testRunCommandPrivateGitHubRepositoryNotInitialCloneNotInteractiveWithAuthentication($gitUrl, $protocol, $gitHubToken, $expectedUrl, $expectedFailuresBeforeSuccess)
     {
         $commandCallable = function ($url) use ($expectedUrl) {
             if ($url !== $expectedUrl) {
@@ -110,13 +109,10 @@ class GitTest extends TestCase
 
         $this->mockConfig($protocol);
 
-        $this->process
-            ->expects($this->atLeast(2))
-            ->method('execute')
-            ->willReturnMap(array(
-                array('git command failing', null, null, 1),
-                array('git command ok', null, null, 0),
-            ));
+        $expectedCalls = array_fill(0, $expectedFailuresBeforeSuccess, array('cmd' => 'git command failing', 'return' => 1));
+        $expectedCalls[] = array('cmd' => 'git command ok', 'return' => 0);
+
+        $this->process->expects($expectedCalls, true);
 
         $this->io
             ->method('isInteractive')
@@ -135,13 +131,15 @@ class GitTest extends TestCase
             ->willReturn(array('username' => 'token', 'password' => $gitHubToken));
 
         $this->git->runCommand($commandCallable, $gitUrl, null, true);
+
+        $this->process->assertComplete($this);
     }
 
     public function privateGithubWithCredentialsProvider()
     {
         return array(
-            array('git@github.com:acme/repo.git', 'ssh', 'MY_GITHUB_TOKEN', 'https://token:MY_GITHUB_TOKEN@github.com/acme/repo.git'),
-            array('https://github.com/acme/repo', 'https', 'MY_GITHUB_TOKEN', 'https://token:MY_GITHUB_TOKEN@github.com/acme/repo.git'),
+            array('git@github.com:acme/repo.git', 'ssh', 'MY_GITHUB_TOKEN', 'https://token:MY_GITHUB_TOKEN@github.com/acme/repo.git', 1),
+            array('https://github.com/acme/repo', 'https', 'MY_GITHUB_TOKEN', 'https://token:MY_GITHUB_TOKEN@github.com/acme/repo.git', 2),
         );
     }