diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
index 4031efea1..9ca5f3ae5 100644
--- a/.php-cs-fixer.php
+++ b/.php-cs-fixer.php
@@ -33,7 +33,6 @@ return $config->setRules([
         'no_blank_lines_after_phpdoc' => true,
         'no_empty_statement' => true,
         'no_extra_blank_lines' => true,
-        'no_leading_import_slash' => true,
         'no_leading_namespace_whitespace' => true,
         'no_trailing_comma_in_singleline_array' => true,
         'no_whitespace_in_blank_line' => true,
@@ -57,7 +56,6 @@ return $config->setRules([
         'no_unused_imports' => true,
         'fully_qualified_strict_types' => true,
         'single_line_after_imports' => true,
-        'fully_qualified_strict_types' => true,
         //'global_namespace_import' => ['import_classes' => true],
         'no_leading_import_slash' => true,
         'single_import_per_statement' => true,
diff --git a/src/Composer/Installer/InstallerInterface.php b/src/Composer/Installer/InstallerInterface.php
index f664a3ab4..fd3015e83 100644
--- a/src/Composer/Installer/InstallerInterface.php
+++ b/src/Composer/Installer/InstallerInterface.php
@@ -111,10 +111,10 @@ interface InstallerInterface
     public function cleanup($type, PackageInterface $package, PackageInterface $prevPackage = null);
 
     /**
-     * Returns the installation path of a package
+     * Returns the absolute installation path of a package.
      *
      * @param  PackageInterface $package
-     * @return string           path to install to, which MUST not end with a slash
+     * @return string           absolute path to install to, which MUST not end with a slash
      */
     public function getInstallPath(PackageInterface $package);
 }
diff --git a/tests/Composer/Test/ConfigTest.php b/tests/Composer/Test/ConfigTest.php
index 579987a52..de00785a2 100644
--- a/tests/Composer/Test/ConfigTest.php
+++ b/tests/Composer/Test/ConfigTest.php
@@ -13,6 +13,7 @@
 namespace Composer\Test;
 
 use Composer\Config;
+use Composer\Util\Platform;
 
 class ConfigTest extends TestCase
 {
@@ -325,22 +326,24 @@ class ConfigTest extends TestCase
 
     public function testProcessTimeout()
     {
-        putenv('COMPOSER_PROCESS_TIMEOUT=0');
+        Platform::putEnv('COMPOSER_PROCESS_TIMEOUT', '0');
         $config = new Config(true);
         $this->assertEquals(0, $config->get('process-timeout'));
-        putenv('COMPOSER_PROCESS_TIMEOUT');
+        Platform::clearEnv('COMPOSER_PROCESS_TIMEOUT');
     }
 
     public function testHtaccessProtect()
     {
-        putenv('COMPOSER_HTACCESS_PROTECT=0');
+        Platform::putEnv('COMPOSER_HTACCESS_PROTECT', '0');
         $config = new Config(true);
         $this->assertEquals(0, $config->get('htaccess-protect'));
-        putenv('COMPOSER_HTACCESS_PROTECT');
+        Platform::clearEnv('COMPOSER_HTACCESS_PROTECT');
     }
 
     public function testGetSourceOfValue()
     {
+        Platform::clearEnv('COMPOSER_PROCESS_TIMEOUT');
+
         $config = new Config;
 
         $this->assertSame(Config::SOURCE_DEFAULT, $config->getSourceOfValue('process-timeout'));
@@ -355,9 +358,9 @@ class ConfigTest extends TestCase
 
     public function testGetSourceOfValueEnvVariables()
     {
-        putenv('COMPOSER_HTACCESS_PROTECT=0');
+        Platform::putEnv('COMPOSER_HTACCESS_PROTECT', '0');
         $config = new Config;
         $this->assertEquals('COMPOSER_HTACCESS_PROTECT', $config->getSourceOfValue('htaccess-protect'));
-        putenv('COMPOSER_HTACCESS_PROTECT');
+        Platform::clearEnv('COMPOSER_HTACCESS_PROTECT');
     }
 }