diff --git a/tests/src/Unit/Utility/FacetsDateHandlerTest.php b/tests/src/Unit/Utility/FacetsDateHandlerTest.php
new file mode 100644
index 0000000..f60edb8
--- /dev/null
+++ b/tests/src/Unit/Utility/FacetsDateHandlerTest.php
@@ -0,0 +1,248 @@
+<?php
+
+/**
+ * @file
+ * Contains \Drupal\Tests\facets\Unit\utility\FacetsDateHandlerTest.
+ */
+
+namespace Drupal\Tests\facets\Unit\utility;
+
+use Drupal\Core\Datetime\DateFormatter;
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Language\Language;
+use Drupal\facets\utility\FacetsDateHandler;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * Unit test for Date Handler Service.
+ *
+ * @group facets
+ */
+class FacetsDateHandlerTest extends UnitTestCase {
+
+  /**
+   * Timestamp used by tests: Thu, 26 Nov 1987 20:43:04 GMT.
+   */
+  const TIMESTAMP = 564957784;
+
+  /**
+   * ISO date used by tests: Thu, 26 Nov 1987 20:43:04 GMT.
+   */
+  const ISO_DATE = '1987-11-26T20:43:04Z';
+
+  /**
+   * The system under test.
+   *
+   * @var \Drupal\facets\utility\FacetsDateHandler
+   */
+  protected $handler;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    $entity_storage = $this->getMock('Drupal\Core\Entity\EntityStorageInterface');
+
+    $em = $this->getMock('Drupal\Core\Entity\EntityManagerInterface');
+    $em->expects($this->any())
+      ->method('getStorage')
+      ->with('date_format')
+      ->willReturn($entity_storage);
+
+    $language = new Language(['id' => 'en']);
+
+    $lm = $this->getMock('Drupal\Core\Language\LanguageManagerInterface');
+    $lm->method('getCurrentLanguage')
+      ->willReturn($language);
+    $st = $this->getMock('Drupal\Core\StringTranslation\TranslationInterface');
+    $rs = $this->getMock('Symfony\Component\HttpFoundation\RequestStack');
+    $cf = $this->getConfigFactoryStub();
+
+    $config_factory = $this->getConfigFactoryStub([
+      'system.date' => ['country' => ['default' => 'GB']],
+    ]);
+    $container = new ContainerBuilder();
+    $container->set('config.factory', $config_factory);
+    \Drupal::setContainer($container);
+
+    $date_formatter = new DateFormatter($em, $lm, $st, $cf, $rs);
+
+    $this->handler = new FacetsDateHandler($date_formatter);
+  }
+
+  /**
+   * Tests the isoDate method.
+   *
+   * @dataProvider provideIsoDates
+   */
+  public function testIsoDate($iso_date, $gap) {
+    $fd = $this->handler;
+    $this->assertEquals($iso_date, $fd->isoDate(static::TIMESTAMP, $gap));
+  }
+
+  /**
+   * Tests for ::getNextDateGap.
+   */
+  public function testGetNextDateGap() {
+    $fd = $this->handler;
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_SECOND);
+    $this->assertEquals($fd::FACETS_DATE_SECOND, $gap);
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_MINUTE);
+    $this->assertEquals($fd::FACETS_DATE_SECOND, $gap);
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_SECOND, $fd::FACETS_DATE_MINUTE);
+    $this->assertEquals($fd::FACETS_DATE_MINUTE, $gap);
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_MINUTE, $fd::FACETS_DATE_MINUTE);
+    $this->assertEquals($fd::FACETS_DATE_MINUTE, $gap);
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_SECOND, $fd::FACETS_DATE_HOUR);
+    $this->assertEquals($fd::FACETS_DATE_HOUR, $gap);
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_MINUTE, $fd::FACETS_DATE_HOUR);
+    $this->assertEquals($fd::FACETS_DATE_HOUR, $gap);
+
+    $gap = $fd->getNextDateGap($fd::FACETS_DATE_HOUR, $fd::FACETS_DATE_HOUR);
+    $this->assertEquals($fd::FACETS_DATE_HOUR, $gap);
+  }
+
+  /**
+   * Tests for ::getTimestampGap.
+   */
+  public function testGetTimestampGap() {
+    $fd = $this->handler;
+
+    // The best search gap between two dates must be a year.
+    $date_gap = $this->handler->getTimestampGap(static::TIMESTAMP, static::TIMESTAMP + 31536000);
+    $this->assertEquals($fd::FACETS_DATE_YEAR, $date_gap);
+
+    // The best search gap between two dates must be a month.
+    $date_gap = $this->handler->getTimestampGap(static::TIMESTAMP, static::TIMESTAMP + 86400 * 60);
+    $this->assertEquals($fd::FACETS_DATE_MONTH, $date_gap);
+
+    // The best search gap between two dates must be a day.
+    $date_gap = $this->handler->getTimestampGap(static::TIMESTAMP, static::TIMESTAMP + 86400);
+    $this->assertEquals($fd::FACETS_DATE_DAY, $date_gap);
+
+    // The best search gap between two dates must be an hour.
+    $date_gap = $this->handler->getTimestampGap(static::TIMESTAMP, static::TIMESTAMP + 3600);
+    $this->assertEquals($fd::FACETS_DATE_HOUR, $date_gap);
+
+    // The best search gap between two dates must be a minute.
+    $date_gap = $this->handler->getTimestampGap(static::TIMESTAMP, static::TIMESTAMP + 60);
+    $this->assertEquals($fd::FACETS_DATE_MINUTE, $date_gap);
+
+    // The best search gap between two dates must be a second.
+    $date_gap = $this->handler->getTimestampGap(static::TIMESTAMP, static::TIMESTAMP + 59);
+    $this->assertEquals($fd::FACETS_DATE_SECOND, $date_gap);
+  }
+
+  /**
+   * Tests for ::getDateGap method.
+   */
+  public function testGetDateGap() {
+    $fd = $this->handler;
+
+    // Cannot convert to timestamp.
+    $this->assertFalse($fd->getDateGap(static::TIMESTAMP, static::TIMESTAMP));
+
+    // The min. gap is MONTH but the result is larger.
+    $this->assertEquals($fd::FACETS_DATE_YEAR, $fd->getDateGap('1983-03-03T20:43:04Z', '1987-11-26T20:43:04Z', $fd::FACETS_DATE_MONTH));
+
+    // The gap is YEAR.
+    $this->assertEquals($fd::FACETS_DATE_YEAR, $fd->getDateGap('1983-03-03T20:43:04Z', '1987-11-26T20:43:04Z'));
+
+    // The gap is MONTH.
+    $this->assertEquals($fd::FACETS_DATE_MONTH, $fd->getDateGap('1983-03-03T20:43:04Z', '1983-11-26T20:43:04Z'));
+
+    // The gap is DAY.
+    $this->assertEquals($fd::FACETS_DATE_DAY, $fd->getDateGap('1983-03-03T20:43:04Z', '1983-03-26T20:43:04Z'));
+
+    // The gap is HOUR.
+    $this->assertEquals($fd::FACETS_DATE_HOUR, $fd->getDateGap('1983-03-03T20:43:04Z', '1983-03-03T21:44:04Z'));
+
+    // The gap is MINUTE.
+    $this->assertEquals($fd::FACETS_DATE_MINUTE, $fd->getDateGap('1983-03-03T20:43:04Z', '1983-03-03T20:44:04Z'));
+
+    // The gap is SECOND.
+    $this->assertEquals($fd::FACETS_DATE_SECOND, $fd->getDateGap('1983-03-03T20:43:04Z', '1983-03-03T20:43:55Z'));
+  }
+
+  /**
+   * Tests for ::nextDateIncrement method.
+   *
+   * @dataProvider provideNextDateIncrementData
+   */
+  public function testNextDateIncrement($incremented_iso_date, $gap) {
+    $this->assertEquals($incremented_iso_date, $this->handler->getNextDateIncrement(static::ISO_DATE, $gap));
+  }
+
+  /**
+   * Tests for ::gapCompare method.
+   */
+  public function testGapCompare() {
+    $fd = $this->handler;
+
+    // Timestamps are equals.
+    $this->assertEquals(0, $fd->gapCompare(static::TIMESTAMP, static::TIMESTAMP));
+
+    // Timestamps are equals.
+    $this->assertEquals(0, $fd->gapCompare($fd::FACETS_DATE_YEAR, $fd::FACETS_DATE_YEAR));
+
+    // gap1 is less than gap2.
+    $this->assertEquals(-1, $fd->gapCompare($fd::FACETS_DATE_MONTH, $fd::FACETS_DATE_YEAR));
+
+    // gap1 is less than gap2.
+    $this->assertEquals(1, $fd->gapCompare($fd::FACETS_DATE_MONTH, $fd::FACETS_DATE_DAY));
+  }
+
+  /**
+   * Tests for ::formatTimestamp method.
+   */
+  public function testFormatTimestamp() {
+    $fd = $this->handler;
+
+    $year = $fd->formatTimestamp(static::TIMESTAMP);
+    $this->assertEquals(1987, $year);
+  }
+
+  /**
+   * Returns a data provider for the ::testIsoDate().
+   *
+   * @return array
+   *   Arrays with data for the test data.
+   */
+  public function provideIsoDates() {
+    return [
+      ['1987-11-26T20:43:04Z', FacetsDateHandler::FACETS_DATE_SECOND],
+      ['1987-11-26T20:43:00Z', FacetsDateHandler::FACETS_DATE_MINUTE],
+      ['1987-11-26T20:00:00Z', FacetsDateHandler::FACETS_DATE_HOUR],
+      ['1987-11-26T00:00:00Z', FacetsDateHandler::FACETS_DATE_DAY],
+      ['1987-11-01T00:00:00Z', FacetsDateHandler::FACETS_DATE_MONTH],
+      ['1987-01-01T00:00:00Z', FacetsDateHandler::FACETS_DATE_YEAR],
+      ['1987-11-26T20:43:04Z', FacetsDateHandler::FACETS_DATE_ISO8601],
+    ];
+  }
+
+  /**
+   * Returns a data provider for the ::testNextDateIncrement().
+   *
+   * @return array
+   *   Arrays with data for the test data.
+   */
+  public function provideNextDateIncrementData() {
+    return [
+      ['1987-11-26T20:43:05Z', FacetsDateHandler::FACETS_DATE_SECOND],
+      ['1987-11-26T20:44:04Z', FacetsDateHandler::FACETS_DATE_MINUTE],
+      ['1987-11-26T21:43:04Z', FacetsDateHandler::FACETS_DATE_HOUR],
+      ['1987-11-27T20:43:04Z', FacetsDateHandler::FACETS_DATE_DAY],
+      ['1987-12-26T20:43:04Z', FacetsDateHandler::FACETS_DATE_MONTH],
+      ['1988-11-26T20:43:04Z', FacetsDateHandler::FACETS_DATE_YEAR],
+    ];
+  }
+
+}