diff --git a/src/parser/__tests__/ArcanistBundleTestCase.php b/src/parser/__tests__/ArcanistBundleTestCase.php
--- a/src/parser/__tests__/ArcanistBundleTestCase.php
+++ b/src/parser/__tests__/ArcanistBundleTestCase.php
@@ -111,14 +111,13 @@
       execx('git reset --hard %s --', $commit_hash);
 
       $fixture_path = $fixture->getPath();
-      $working_copy = ArcanistWorkingCopyIdentity::newFromPath($fixture_path);
+      $working_copy = ArcanistWorkingCopy::newFromWorkingDirectory(
+        $fixture_path);
 
-      $configuration_manager = new ArcanistConfigurationManager();
-      $configuration_manager->setWorkingCopyIdentity($working_copy);
-      $repository_api = ArcanistRepositoryAPI::newAPIFromConfigurationManager(
-        $configuration_manager);
+      $repository_api = $working_copy->newRepositoryAPI();
 
       $repository_api->setBaseCommitArgumentRules('arc:this');
+
       $diff = $repository_api->getFullGitDiff(
         $repository_api->getBaseCommit(),
         $repository_api->getHeadCommit());
diff --git a/src/repository/api/ArcanistRepositoryAPI.php b/src/repository/api/ArcanistRepositoryAPI.php
--- a/src/repository/api/ArcanistRepositoryAPI.php
+++ b/src/repository/api/ArcanistRepositoryAPI.php
@@ -657,9 +657,8 @@
       'user'    => '',
       'system'  => '',
     );
-    $all_sources = $this->configurationManager->getConfigFromAllSources('base');
 
-    $base_commit_rules = $all_sources + $base_commit_rules;
+    // TOOLSETS: Handle "base" configuration.
 
     $parser = new ArcanistBaseCommitParser($this);
     $commit = $parser->resolveBaseCommit($base_commit_rules);