Skip Mercurial tests if hg is not present

Summary: I don't have `hg` yet on my new laptop; we should just skip tests if the user is missing binaries. Add a convenience method to do this.

Test Plan: Got clean `arc unit --everything` with no `hg` installed.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11051

src/applications/repository/engine/__tests__/PhabricatorWorkingCopyDiscoveryTestCase.php

@@ -15,6 +15,8 @@ final class PhabricatorWorkingCopyDiscoveryTestCase
   }
 
   public function testMercurialCommitDiscovery() {
+    $this->requireBinaryForTest('hg');
+
     $refs = $this->discoverRefs('HT');
     $this->assertEqual(
       array(

src/applications/repository/engine/__tests__/PhabricatorWorkingCopyPullTestCase.php

@@ -10,6 +10,7 @@ final class PhabricatorWorkingCopyPullTestCase
   }
 
   public function testHgPullBasic() {
+    $this->requireBinaryForTest('hg');
     $repo = $this->buildPulledRepository('HT');
 
     $this->assertTrue(Filesystem::pathExists($repo->getLocalPath().'/.hg'));

src/applications/repository/worker/__tests__/PhabricatorChangeParserTestCase.php

@@ -203,6 +203,8 @@ final class PhabricatorChangeParserTestCase
   }
 
   public function testMercurialParser() {
+    $this->requireBinaryForTest('hg');
+
     $repository = $this->buildDiscoveredRepository('CHB');
     $viewer = PhabricatorUser::getOmnipotentUser();
 

src/infrastructure/testing/PhabricatorTestCase.php

@@ -218,5 +218,12 @@ abstract class PhabricatorTestCase extends ArcanistPhutilTestCase {
     }
   }
 
+  protected function requireBinaryForTest($binary) {
+    if (!Filesystem::binaryExists($binary)) {
+      $this->assertSkipped(
+        pht('No binary "%s" found on this system, skipping test.', $binary));
+    }
+  }
+
 
 }