diff --git a/tests/Composer/Test/Installer/LibraryInstallerTest.php b/tests/Composer/Test/Installer/LibraryInstallerTest.php
index ad933dcaa..11ed529c4 100644
--- a/tests/Composer/Test/Installer/LibraryInstallerTest.php
+++ b/tests/Composer/Test/Installer/LibraryInstallerTest.php
@@ -13,6 +13,7 @@
 namespace Composer\Test\Installer;
 
 use Composer\Installer\LibraryInstaller;
+use Composer\Repository\InstalledArrayRepository;
 use Composer\Util\Filesystem;
 use Composer\Test\TestCase;
 use Composer\Composer;
@@ -121,16 +122,21 @@ class LibraryInstallerTest extends TestCase
     public function testIsInstalled(): void
     {
         $library = new LibraryInstaller($this->io, $this->composer);
-        $package = $this->createPackageMock();
+        $package = $this->getPackage('test/pkg', '1.0.0');
 
-        $this->repository
-            ->expects($this->exactly(2))
-            ->method('hasPackage')
-            ->with($package)
-            ->will($this->onConsecutiveCalls(true, false));
+        $repository = new InstalledArrayRepository();
+        $this->assertFalse($library->isInstalled($repository, $package));
 
-        $this->assertTrue($library->isInstalled($this->repository, $package));
-        $this->assertFalse($library->isInstalled($this->repository, $package));
+        // package being in repo is not enough to be installed
+        $repository->addPackage($package);
+        $this->assertFalse($library->isInstalled($repository, $package));
+
+        // package being in repo and vendor/pkg/foo dir present means it is seen as installed
+        $this->ensureDirectoryExistsAndClear($this->vendorDir.'/'.$package->getPrettyName());
+        $this->assertTrue($library->isInstalled($repository, $package));
+
+        $repository->removePackage($package);
+        $this->assertFalse($library->isInstalled($repository, $package));
     }
 
     /**
@@ -140,12 +146,7 @@ class LibraryInstallerTest extends TestCase
     public function testInstall(): void
     {
         $library = new LibraryInstaller($this->io, $this->composer);
-        $package = $this->createPackageMock();
-
-        $package
-            ->expects($this->any())
-            ->method('getPrettyName')
-            ->will($this->returnValue('some/package'));
+        $package = $this->getPackage('some/package', '1.0.0');
 
         $this->dm
             ->expects($this->once())
@@ -173,30 +174,13 @@ class LibraryInstallerTest extends TestCase
         $filesystem
           ->expects($this->once())
           ->method('rename')
-          ->with($this->vendorDir.'/package1/oldtarget', $this->vendorDir.'/package1/newtarget');
+          ->with($this->vendorDir.'/vendor/package1/oldtarget', $this->vendorDir.'/vendor/package1/newtarget');
 
-        $initial = $this->createPackageMock();
-        $target = $this->createPackageMock();
+        $initial = $this->getPackage('vendor/package1', '1.0.0');
+        $target = $this->getPackage('vendor/package1', '2.0.0');
 
-        $initial
-            ->expects($this->any())
-            ->method('getPrettyName')
-            ->will($this->returnValue('package1'));
-
-        $initial
-            ->expects($this->any())
-            ->method('getTargetDir')
-            ->will($this->returnValue('oldtarget'));
-
-        $target
-            ->expects($this->any())
-            ->method('getPrettyName')
-            ->will($this->returnValue('package1'));
-
-        $target
-            ->expects($this->any())
-            ->method('getTargetDir')
-            ->will($this->returnValue('newtarget'));
+        $initial->setTargetDir('oldtarget');
+        $target->setTargetDir('newtarget');
 
         $this->repository
             ->expects($this->exactly(3))
@@ -206,7 +190,7 @@ class LibraryInstallerTest extends TestCase
         $this->dm
             ->expects($this->once())
             ->method('update')
-            ->with($initial, $target, $this->vendorDir.'/package1/newtarget');
+            ->with($initial, $target, $this->vendorDir.'/vendor/package1/newtarget');
 
         $this->repository
             ->expects($this->once())
@@ -231,16 +215,7 @@ class LibraryInstallerTest extends TestCase
     public function testUninstall(): void
     {
         $library = new LibraryInstaller($this->io, $this->composer);
-        $package = $this->createPackageMock();
-
-        $package
-            ->expects($this->any())
-            ->method('getPrettyName')
-            ->will($this->returnValue('pkg'));
-        $package
-            ->expects($this->any())
-            ->method('getName')
-            ->will($this->returnValue('pkg'));
+        $package = $this->getPackage('vendor/pkg', '1.0.0');
 
         $this->repository
             ->expects($this->exactly(2))
@@ -251,7 +226,7 @@ class LibraryInstallerTest extends TestCase
         $this->dm
             ->expects($this->once())
             ->method('remove')
-            ->with($package, $this->vendorDir.'/pkg');
+            ->with($package, $this->vendorDir.'/vendor/pkg');
 
         $this->repository
             ->expects($this->once())
@@ -265,32 +240,19 @@ class LibraryInstallerTest extends TestCase
         $library->uninstall($this->repository, $package);
     }
 
-    public function testGetInstallPath(): void
+    public function testGetInstallPathWithoutTargetDir(): void
     {
         $library = new LibraryInstaller($this->io, $this->composer);
-        $package = $this->createPackageMock();
+        $package = $this->getPackage('Vendor/Pkg', '1.0.0');
 
-        $package
-            ->expects($this->once())
-            ->method('getTargetDir')
-            ->will($this->returnValue(null));
-
-        $this->assertEquals($this->vendorDir.'/'.$package->getName(), $library->getInstallPath($package));
+        $this->assertEquals($this->vendorDir.'/'.$package->getPrettyName(), $library->getInstallPath($package));
     }
 
     public function testGetInstallPathWithTargetDir(): void
     {
         $library = new LibraryInstaller($this->io, $this->composer);
-        $package = $this->createPackageMock();
-
-        $package
-            ->expects($this->once())
-            ->method('getTargetDir')
-            ->will($this->returnValue('Some/Namespace'));
-        $package
-            ->expects($this->any())
-            ->method('getPrettyName')
-            ->will($this->returnValue('foo/bar'));
+        $package = $this->getPackage('Foo/Bar', '1.0.0');
+        $package->setTargetDir('Some/Namespace');
 
         $this->assertEquals($this->vendorDir.'/'.$package->getPrettyName().'/Some/Namespace', $library->getInstallPath($package));
     }
@@ -306,7 +268,7 @@ class LibraryInstallerTest extends TestCase
             ->getMock();
 
         $library = new LibraryInstaller($this->io, $this->composer, 'library', null, $binaryInstallerMock);
-        $package = $this->createPackageMock();
+        $package = $this->getPackage('foo/bar', '1.0.0');
 
         $binaryInstallerMock
             ->expects($this->never())
@@ -320,14 +282,4 @@ class LibraryInstallerTest extends TestCase
 
         $library->ensureBinariesPresence($package);
     }
-
-    /**
-     * @return \Composer\Package\PackageInterface&\PHPUnit\Framework\MockObject\MockObject
-     */
-    protected function createPackageMock()
-    {
-        return $this->getMockBuilder('Composer\Package\Package')
-            ->setConstructorArgs(array(md5((string) mt_rand()), '1.0.0.0', '1.0.0'))
-            ->getMock();
-    }
 }