diff --git a/core/modules/field/src/Plugin/migrate/process/d6/FieldTypeDefaults.php b/core/modules/field/src/Plugin/migrate/process/d6/FieldTypeDefaults.php
index 1f6e2f3..eb2a97f 100644
--- a/core/modules/field/src/Plugin/migrate/process/d6/FieldTypeDefaults.php
+++ b/core/modules/field/src/Plugin/migrate/process/d6/FieldTypeDefaults.php
@@ -30,7 +30,7 @@ public function transform($value, MigrateExecutableInterface $migrate_executable
         $value = 'datetime_default';
       }
       else {
-        throw new MigrateException(sprintf('Failed to lookup %s in the static map.', var_export($value, TRUE)));
+        throw new MigrateException(sprintf('Failed to lookup field type %s in the static map.', var_export($value, TRUE)));
       }
     }
     return $value;
diff --git a/core/modules/field/tests/src/Unit/Plugin/migrate/process/d6/FieldTypeDefaultsTest.php b/core/modules/field/tests/src/Unit/Plugin/migrate/process/d6/FieldTypeDefaultsTest.php
new file mode 100644
index 0000000..814f886
--- /dev/null
+++ b/core/modules/field/tests/src/Unit/Plugin/migrate/process/d6/FieldTypeDefaultsTest.php
@@ -0,0 +1,59 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\field\Unit\Plugin\migrate\process\d6\FieldTypeDefaultsTest.
+ */
+
+namespace Drupal\Tests\field\Unit\Plugin\migrate\process\d6;
+
+use Drupal\field\Plugin\migrate\process\d6\FieldTypeDefaults;
+use Drupal\migrate\MigrateException;
+use Drupal\Tests\migrate\Unit\process\MigrateProcessTestCase;
+
+/**
+ * Tests D6 fields defaults.
+ *
+ * @coversDefaultClass \Drupal\field\Plugin\migrate\process\d6\FieldTypeDefaults
+ * @group field
+ */
+class FieldTypeDefaultsTest extends MigrateProcessTestCase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+    $this->plugin = new FieldTypeDefaults([], 'field_type_defaults', []);
+  }
+
+  /**
+   * Test various default cases.
+   *
+   * @covers ::transform
+   */
+  public function testDefaults() {
+    $this->row->expects($this->once())
+      ->method('getSourceProperty')
+      ->willReturn('date');
+
+    // Assert common values are passed through without modification.
+    $this->assertNull($this->plugin->transform(NULL, $this->migrateExecutable, $this->row, 'property'));
+    $this->assertEquals('string', $this->plugin->transform('string', $this->migrateExecutable, $this->row, 'property'));
+    $this->assertEquals(1234, $this->plugin->transform(1234, $this->migrateExecutable, $this->row, 'property'));
+    // Assert that an array checks that this is a date field(above mock assert)
+    // and returns "datetime_default".
+    $this->assertEquals('datetime_default', $this->plugin->transform([], $this->migrateExecutable, $this->row, 'property'));
+  }
+
+  /**
+   * When given an array that is not a date field we throw an exception.
+   *
+   * @covers ::transform
+   */
+  public function testDefaultsException() {
+    $this->setExpectedException(MigrateException::class,
+      sprintf('Failed to lookup field type %s in the static map.', var_export([], TRUE)));
+    $this->plugin->transform([], $this->migrateExecutable, $this->row, 'property');
+  }
+}