diff --git a/src/TestUtils/TestTrait.php b/src/TestUtils/TestTrait.php
index 8f870c1..e9a7763 100644
--- a/src/TestUtils/TestTrait.php
+++ b/src/TestUtils/TestTrait.php
@@ -57,17 +57,21 @@ private static function runSnippet($sampleName, $params = [])
         }
 
         $testFunc = function () use ($sampleFile, $params) {
-            return shell_exec(sprintf(
-                'php %s %s',
-                $sampleFile,
-                implode(' ', array_map('escapeshellarg', $params))
-            ));
+            $argv = array_merge([$sampleFile], $params);
+            $argc = count($argv);
+            try {
+                ob_start();
+                require $sampleFile;
+                return ob_get_clean();
+            } catch (\Exception $e) {
+                ob_get_clean();
+                throw $e;
+            }
         };
 
         if (isset(self::$backoff)) {
             return self::$backoff->execute($testFunc);
         }
-
         return $testFunc();
     }
 }
diff --git a/test/TestUtils/TestTraitTest.php b/test/TestUtils/TestTraitTest.php
index 861be9d..4ff7a8a 100644
--- a/test/TestUtils/TestTraitTest.php
+++ b/test/TestUtils/TestTraitTest.php
@@ -18,6 +18,7 @@
 namespace Google\Cloud\TestUtils\test;
 
 use Google\Cloud\TestUtils\TestTrait;
+use Google\Cloud\TestUtils\ExponentialBackoffTrait;
 
 /**
  * Class TestTraitTest
@@ -28,8 +29,7 @@
 class TestTraitTest extends \PHPUnit_Framework_TestCase
 {
     use TestTrait;
-
-    private static $backoff;
+    use ExponentialBackoffTrait;
 
     public static function checkProjectEnvVarBeforeClass()
     {
@@ -108,18 +108,41 @@ public function testRunSnippet()
         $output1 = shell_exec($snippet2Cmd . ' foo bar baz');
         $output2 = $this->runSnippet($snippet2File, ['foo', 'bar', 'baz']);
         $this->assertEquals($output1, $output2);
+    }
+
+    public function testRunSnippetWithBackoff()
+    {
+        $this->useBackoff($retries = 5, function () use (&$timesCalled) {
+            $timesCalled++;
+            return true;
+        });
+
+        self::setDelayFunction(function ($delay) {
+            // do nothing!
+        });
+
+        try {
+            $output = $this->runSnippet('snippet3');
+            $this->fail('Should have thrown exception');
+        } catch (\Exception $e) {
+            $this->assertEquals('This is expected', $e->getMessage());
+        }
 
-        self::$backoff = new FakeBackoff();
+        $this->assertEquals($retries + 1, $timesCalled);
+    }
 
-        $output = $this->runSnippet('foo');
-        $this->assertEquals('FakeBackoff', $output);
+    /**
+     * @expectedException Exception
+     * @expectedExceptionMessage This is expected
+     */
+    public function testRunSnippetWithException()
+    {
+        $this->runSnippet('snippet3');
     }
-}
 
-class FakeBackoff
-{
-    public function execute($fn)
+    public function setUp()
     {
-        return "FakeBackoff";
+        // Clear backoffs before running each test
+        self::$backoff = null;
     }
 }
diff --git a/test/src/snippet3.php b/test/src/snippet3.php
new file mode 100644
index 0000000..b7010a5
--- /dev/null
+++ b/test/src/snippet3.php
@@ -0,0 +1,3 @@
+<?php
+
+throw new Exception('This is expected');