Updated the tests to match the new command that is executed

tests/Composer/Test/Downloader/GitDownloaderTest.php

@@ -371,7 +371,7 @@ class GitDownloaderTest extends TestCase
 
     public function testUpdate()
     {
-        $expectedGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git fetch composer && git fetch --tags composer");
+        $expectedGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git rev-parse --quiet --verify 'ref'^{commit} || (git fetch composer && git fetch --tags composer)");
 
         $packageMock = $this->getMock('Composer\Package\PackageInterface');
         $packageMock->expects($this->any())
@@ -420,7 +420,7 @@ class GitDownloaderTest extends TestCase
 
     public function testUpdateWithNewRepoUrl()
     {
-        $expectedGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git fetch composer && git fetch --tags composer");
+        $expectedGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git rev-parse --quiet --verify 'ref'^{commit} || (git fetch composer && git fetch --tags composer)");
 
         $packageMock = $this->getMock('Composer\Package\PackageInterface');
         $packageMock->expects($this->any())
@@ -491,7 +491,7 @@ composer https://github.com/old/url (push)
      */
     public function testUpdateThrowsRuntimeExceptionIfGitCommandFails()
     {
-        $expectedGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git fetch composer && git fetch --tags composer");
+        $expectedGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git rev-parse --quiet --verify 'ref'^{commit} || (git fetch composer && git fetch --tags composer)");
 
         $packageMock = $this->getMock('Composer\Package\PackageInterface');
         $packageMock->expects($this->any())
@@ -529,8 +529,8 @@ composer https://github.com/old/url (push)
 
     public function testUpdateDoesntThrowsRuntimeExceptionIfGitCommandFailsAtFirstButIsAbleToRecover()
     {
-        $expectedFirstGitUpdateCommand = $this->winCompat("git remote set-url composer '' && git fetch composer && git fetch --tags composer");
-        $expectedSecondGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git fetch composer && git fetch --tags composer");
+        $expectedFirstGitUpdateCommand = $this->winCompat("git remote set-url composer '' && git rev-parse --quiet --verify 'ref'^{commit} || (git fetch composer && git fetch --tags composer)");
+        $expectedSecondGitUpdateCommand = $this->winCompat("git remote set-url composer 'https://github.com/composer/composer' && git rev-parse --quiet --verify 'ref'^{commit} || (git fetch composer && git fetch --tags composer)");
 
         $packageMock = $this->getMock('Composer\Package\PackageInterface');
         $packageMock->expects($this->any())