diff --git a/src/unit/engine/ArcanistConfigurationDrivenUnitTestEngine.php b/src/unit/engine/ArcanistConfigurationDrivenUnitTestEngine.php
--- a/src/unit/engine/ArcanistConfigurationDrivenUnitTestEngine.php
+++ b/src/unit/engine/ArcanistConfigurationDrivenUnitTestEngine.php
@@ -81,13 +81,11 @@
       }
 
       try {
+        // TODO: Perhaps we should emit a warning if child engines re-use keys
+        // from the defaults, since their specs will not be respected.
         PhutilTypeSpec::checkMap(
           $spec,
-          array(
-            'type' => 'string',
-            'include' => 'optional regex | list<regex>',
-            'exclude' => 'optional regex | list<regex>',
-          ));
+          $this->getDefaultEngineOptions() + $test_engine->getEngineOptions());
       } catch (PhutilTypeCheckException $ex) {
         throw new PhutilProxyException(
           pht(
@@ -108,12 +106,26 @@
         $test_engine->setPaths($paths);
       }
 
+      // Apply any values found from `getEngineOptions` to the engine
+      foreach ($test_engine->getEngineOptions() as $key => $type) {
+        $value = idx($spec, $key, '');
+        $test_engine->setOption($key, $value);
+      }
+
       $built_test_engines[] = $test_engine;
     }
 
     return $built_test_engines;
   }
 
+  private function getDefaultEngineOptions() {
+    return array(
+      'type' => 'string',
+      'include' => 'optional regex | list<regex>',
+      'exclude' => 'optional regex | list<regex>',
+    );
+  }
+
   public function run() {
     $renderer = $this->renderer;
     $this->setRenderer(null);
@@ -150,7 +162,7 @@
         foreach ($results as $result) {
           // If the proxied engine renders its own test results then there
           // is no need to render them again here.
-          if (!$engine->shouldEchoTestResults()) {
+          if ($engine->shouldEchoTestResults()) {
             echo $renderer->renderUnitResult($result);
           }
         }
diff --git a/src/unit/engine/ArcanistUnitTestEngine.php b/src/unit/engine/ArcanistUnitTestEngine.php
--- a/src/unit/engine/ArcanistUnitTestEngine.php
+++ b/src/unit/engine/ArcanistUnitTestEngine.php
@@ -10,6 +10,7 @@
   private $enableCoverage;
   private $runAllTests;
   private $configurationManager;
+  private $options = array();
   protected $renderer;
 
   final public function __construct() {}
@@ -18,6 +19,23 @@
     return null;
   }
 
+  /**
+   * Modify the return value of this function to accept configuration values
+   * from `.arcunit`. Must be in the form used by `PhutilTypeSpec`.
+   */
+  public function getEngineOptions() {
+    return array();
+  }
+
+  final protected function getOption($key, $default = null) {
+    return idx($this->options, $key, $default);
+  }
+
+  final protected function setOption($key, $value) {
+    $this->options[$key] = $value;
+    return $this;
+  }
+
   final public function setRunAllTests($run_all_tests) {
     if (!$this->supportsRunAllTests() && $run_all_tests) {
       throw new Exception(
diff --git a/src/unit/engine/PhpunitTestEngine.php b/src/unit/engine/PhpunitTestEngine.php
--- a/src/unit/engine/PhpunitTestEngine.php
+++ b/src/unit/engine/PhpunitTestEngine.php
@@ -9,6 +9,11 @@
   private $phpunitBinary = 'phpunit';
   private $affectedTests;
   private $projectRoot;
+  private $flags = [];
+
+  public function getEngineConfigurationName() {
+    return 'phpunit';
+  }
 
   public function run() {
     $this->projectRoot = $this->getWorkingCopy()->getProjectRoot();
@@ -45,14 +50,23 @@
       throw new ArcanistNoEffectException(pht('No tests to run.'));
     }
 
-    $this->prepareConfigFile();
+    $this->prepareConfig();
+    if (!Filesystem::binaryExists($this->phpunitBinary)) {
+      throw new Exception(pht(
+        "PHPUnit binary not found at '%s'",
+        $this->phpunitBinary));
+    }
+
     $futures = array();
     $tmpfiles = array();
+
+    $all_flags = implode(' ', $this->flags);
     foreach ($this->affectedTests as $class_path => $test_path) {
       if (!Filesystem::pathExists($test_path)) {
         continue;
       }
       $json_tmp = new TempFile();
+      $json = csprintf('--log-json %s', $json_tmp);
       $clover_tmp = null;
       $clover = null;
       if ($this->getEnableCoverage() !== false) {
@@ -60,12 +74,8 @@
         $clover = csprintf('--coverage-clover %s', $clover_tmp);
       }
 
-      $config = $this->configFile ? csprintf('-c %s', $this->configFile) : null;
-
-      $stderr = '-d display_errors=stderr';
-
-      $futures[$test_path] = new ExecFuture('%C %C %C --log-json %s %C %s',
-        $this->phpunitBinary, $config, $stderr, $json_tmp, $clover, $test_path);
+      $futures[$test_path] = new ExecFuture('%C %C %C %C %s',
+        $this->phpunitBinary, $all_flags, $json, $clover, $test_path);
       $tmpfiles[$test_path] = array(
         'json' => $json_tmp,
         'clover' => $clover_tmp,
@@ -248,17 +258,42 @@
   }
 
   /**
-   * Tries to find and update phpunit configuration file based on
-   * `phpunit_config` option in `.arcconfig`.
+   * Apply configuration values from all possible sources
    */
-  private function prepareConfigFile() {
+  private function prepareConfig() {
+    // .arcconfig, .arcrc, etc.
+    $manager = $this->getConfigurationManager();
+    if ($manager) {
+      $this->prepareConfigFromManager($manager);
+    }
+    // .arcunit
+    foreach ($this->getOption('flags', array()) as $k => $v) {
+      $v = str_replace('$ROOT', $this->projectRoot, $v);
+      $this->flags[] = (string)csprintf('%C %s', $k, $v);
+    }
+    if ($bin = $this->getOption('binary')) {
+      $this->setBinaryPath($bin);
+    }
+
+    // Try to avoid errors in tests from being suppressed (TODO: leave this as
+    // an exercise to the person configuring the engine?)
+    $this->flags[] = '-d display_errors=stderr';
+  }
+
+  /**
+   * Apply configuration from working copy configs. Eventually this may be
+   * deprecated in favor of `.arcunit`.
+   */
+  private function prepareConfigFromManager(
+    ArcanistConfigurationManager $manager) {
     $project_root = $this->projectRoot.DIRECTORY_SEPARATOR;
-    $config = $this->getConfigurationManager()->getConfigFromAnySource(
+    $config = $manager->getConfigFromAnySource(
       'phpunit_config');
 
     if ($config) {
       if (Filesystem::pathExists($project_root.$config)) {
-        $this->configFile = $project_root.$config;
+        $this->flags[] = (string)csprintf('%C %s',
+          '--configuration', $project_root.$config);
       } else {
         throw new Exception(
           pht(
@@ -266,15 +301,30 @@
             $project_root.$config));
       }
     }
-    $bin = $this->getConfigurationManager()->getConfigFromAnySource(
+    $bin = $manager->getConfigFromAnySource(
       'unit.phpunit.binary');
     if ($bin) {
-      if (Filesystem::binaryExists($bin)) {
-        $this->phpunitBinary = $bin;
-      } else {
-        $this->phpunitBinary = Filesystem::resolvePath($bin, $project_root);
-      }
+      $this->setBinaryPath($bin);
+    }
+  }
+
+  public function getEngineOptions() {
+    return array(
+      'flags' => 'optional map<string, string>',
+      'binary' => 'optional string',
+    );
+  }
+
+  private function setBinaryPath($bin) {
+    // Try exactly as-is
+    if (Filesystem::binaryExists($bin)) {
+      $this->phpunitBinary = $bin;
+    } else {
+      // This may resolve wrong, but we check before run that the binary exists.
+      // It's done there instead of here so the default value is also checked.
+      $this->phpunitBinary = Filesystem::resolvePath($bin, $this->projectRoot);
     }
+    return $this;
   }
 
 }
diff --git a/src/unit/engine/PhutilUnitTestEngine.php b/src/unit/engine/PhutilUnitTestEngine.php
--- a/src/unit/engine/PhutilUnitTestEngine.php
+++ b/src/unit/engine/PhutilUnitTestEngine.php
@@ -221,4 +221,9 @@
     return $paths;
   }
 
+  public function shouldEchoTestResults() {
+    // If a renderer exists, PhutilTestCase will automatically render itself;
+    // otherwise, expect an upstream renderer to handle this.
+    return !$this->renderer;
+  }
 }