diff --git a/core/modules/migrate/tests/src/Unit/process/ConcatTest.php b/core/modules/migrate/tests/src/Unit/process/ConcatTest.php
index ea93e46..8d037b0 100644
--- a/core/modules/migrate/tests/src/Unit/process/ConcatTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/ConcatTest.php
@@ -1,10 +1,5 @@
 <?php
 
-/**
- * @file
- * Contains \Drupal\Tests\migrate\Unit\process\ConcatTest.
- */
-
 namespace Drupal\Tests\migrate\Unit\process;
 
 use Drupal\migrate\MigrateException;
@@ -18,52 +13,73 @@
 class ConcatTest extends MigrateProcessTestCase {
 
   /**
-   * {@inheritdoc}
+   * Test concat works without a delimiter.
+   *
+   * @dataProvider providerConcatWithoutDelimiter
    */
-  protected function setUp() {
-    $this->plugin = new TestConcat();
-    parent::setUp();
+  public function testConcatWithoutDelimiter($input, $expected, $configuration = []) {
+    $this->plugin = new Concat($configuration, '', []);
+    $value = $this->plugin->transform($input, $this->migrateExecutable, $this->row, 'destinationproperty');
+    $this->assertSame($expected, $value);
   }
 
   /**
-   * Test concat works without a delimiter.
+   * Data provider for testConcatWithoutDelimiter().
    */
-  public function testConcatWithoutDelimiter() {
-    $value = $this->plugin->transform(['foo', 'bar'], $this->migrateExecutable, $this->row, 'destinationproperty');
-    $this->assertSame($value, 'foobar');
+  public function providerConcatWithoutDelimiter() {
+    return [
+      'no configuration' => [['foo', 'bar'], 'foobar'],
+      'with delimiter' => [['foo', 'bar'], 'foo_bar', ['delimiter' => '_']],
+      'no delimiter, allow_empty is false' => [
+        ['foo', NULL, 'bar'],
+        'foobar',
+        ['allow_empty' => FALSE]
+      ],
+      'no delimiter, allow_empty is true' => [
+        ['foo', NULL, 'bar'],
+        'foobar',
+        ['allow_empty' => TRUE]
+      ],
+      'with delimiter, allow_empty is false, NULL' => [
+        ['foo', NULL, 'bar'],
+        'foo_bar',
+        ['delimiter' => '_', 'allow_empty' => FALSE]
+      ],
+      'with delimiter, allow_empty is true, NULL' => [
+        ['foo', NULL, 'bar'],
+        'foo__bar',
+        ['delimiter' => '_', 'allow_empty' => TRUE]
+      ],
+      'with delimiter, allow_empty is false, empty string' => [
+        ['foo', '', 'bar'],
+        'foo_bar',
+        ['delimiter' => '_', 'allow_empty' => FALSE]
+      ],
+      'with delimiter, allow_empty is true, empty string' => [
+        ['foo', '', 'bar'],
+        'foo__bar',
+        ['delimiter' => '_', 'allow_empty' => TRUE]
+      ],
+      'with delimiter, allow_empty is true, zero' => [
+        ['foo', 0, 'bar'],
+        'foo_0_bar',
+        ['delimiter' => '_', 'allow_empty' => TRUE]
+      ],
+      'with delimiter, allow_empty is true, space' => [
+        ['foo', ' ', 'bar'],
+        'foo_ _bar',
+        ['delimiter' => '_', 'allow_empty' => TRUE]
+      ],
+    ];
   }
 
   /**
    * Test concat fails properly on non-arrays.
    */
   public function testConcatWithNonArray() {
+    $this->plugin = new Concat([], '', []);
     $this->setExpectedException(MigrateException::class);
     $this->plugin->transform('foo', $this->migrateExecutable, $this->row, 'destinationproperty');
   }
 
-  /**
-   * Test concat works without a delimiter.
-   */
-  public function testConcatWithDelimiter() {
-    $this->plugin->setDelimiter('_');
-    $value = $this->plugin->transform(['foo', 'bar'], $this->migrateExecutable, $this->row, 'destinationproperty');
-    $this->assertSame($value, 'foo_bar');
-  }
-
-}
-
-class TestConcat extends Concat {
-  public function __construct() {
-  }
-
-  /**
-   * Set the delimiter.
-   *
-   * @param string $delimiter
-   *   The new delimiter.
-   */
-  public function setDelimiter($delimiter) {
-    $this->configuration['delimiter'] = $delimiter;
-  }
-
 }