diff --git a/src/Console/Command/YamlMungeCommand.php b/src/Console/Command/YamlMungeCommand.php
index ccbcba0ed5..018d6def82 100644
--- a/src/Console/Command/YamlMungeCommand.php
+++ b/src/Console/Command/YamlMungeCommand.php
@@ -60,7 +60,7 @@ protected function munge($file1, $file2) {
     $file1_contents = (array) $this->parseFile($file1);
     $file2_contents = (array) $this->parseFile($file2);
 
-    $munged_contents = $this->arrayMergeRecursiveExceptEmpty($file1_contents, $file2_contents);
+    $munged_contents = self::arrayMergeRecursiveExceptEmpty($file1_contents, $file2_contents);
 
     return Yaml::dump($munged_contents, 3, 2);
   }
@@ -100,12 +100,12 @@ protected function parseFile($file) {
    *
    * @return array
    */
-  protected function arrayMergeRecursiveExceptEmpty(array &$array1, array &$array2) {
+  public static function arrayMergeRecursiveExceptEmpty(array &$array1, array &$array2) {
     $merged = $array1;
 
     foreach ($array2 as $key => &$value) {
       if (is_array($value) && isset($merged[$key]) && is_array($merged[$key]) && !empty($value)) {
-        $merged[$key] = $this->arrayMergeRecursiveExceptEmpty($merged[$key], $value);
+        $merged[$key] = self::arrayMergeRecursiveExceptEmpty($merged[$key], $value);
       }
       else {
         $merged[$key] = $value;
diff --git a/tests/phpunit/Blt/YamlMungeCommandTest.php b/tests/phpunit/Blt/YamlMungeCommandTest.php
new file mode 100644
index 0000000000..e487ade5e3
--- /dev/null
+++ b/tests/phpunit/Blt/YamlMungeCommandTest.php
@@ -0,0 +1,62 @@
+<?php
+
+namespace Acquia\Blt\Tests\Blt;
+
+use Acquia\Blt\Console\Command\YamlMungeCommand;
+use Acquia\Blt\Tests\BltTestBase;
+
+class YamlMungeCommandTest extends \PHPUnit_Framework_TestCase {
+
+  /**
+   * Tests arrayMergeRecursiveExceptEmpty().
+   *
+   * @dataProvider getValueProvider
+   */
+  public function testArrayMergeRecursiveExceptEmpty($array1, $array2, $expected_array) {
+    $this->assertEquals(YamlMungeCommand::arrayMergeRecursiveExceptEmpty($array1, $array2), $expected_array);
+  }
+
+  /**
+   * Provides values to testArrayMergeRecursiveExceptEmpty().
+   *
+   * @return array
+   *   An array of values to test.
+   */
+  public function getValueProvider()
+  {
+
+    return [
+      [
+        [
+          'modules' => [
+            'local' => [ 'test' ],
+            'ci' => [ 'shield'],
+          ],
+          'behat' => [
+            'tags' => 'test',
+            'launch-selenium' => 'true',
+          ],
+        ],
+        [
+          'modules' => [
+            'local' => [ ],
+            'ci' => [ 'shield'],
+          ],
+          'behat' => [
+            'tags' => 'nottest'
+          ]
+        ],
+        [
+          'modules' => [
+            'local' => [ ],
+            'ci' => [ 'shield' ],
+          ],
+          'behat' => [
+            'tags' => 'nottest',
+            'launch-selenium' => 'true',
+          ]
+        ],
+      ],
+    ];
+  }
+}