diff --git a/drupalci.yml b/drupalci.yml
index 19dcb12..733cc5a 100644
--- a/drupalci.yml
+++ b/drupalci.yml
@@ -12,3 +12,7 @@ build:
     validate_codebase:
       phplint:
       phpcs:
+    testing:
+      run_tests.standard:
+        types: 'PHPUnit-Unit,PHPUnit-Kernel,PHPUnit-Functional'
+        suppress-deprecations: false
diff --git a/tests/src/Unit/Plugin/Validation/Constraint/UsernameFormatConstraintValidatorTest.php b/tests/src/Unit/Plugin/Validation/Constraint/UsernameFormatConstraintValidatorTest.php
new file mode 100644
index 0000000..727d2a2
--- /dev/null
+++ b/tests/src/Unit/Plugin/Validation/Constraint/UsernameFormatConstraintValidatorTest.php
@@ -0,0 +1,70 @@
+<?php
+
+namespace Drupal\Tests\do_username\Unit\Plugin\Validation\Constraint;
+
+use Drupal\do_username\Plugin\Field\FieldType\DrupalOrgUsernameItem;
+use Drupal\do_username\Plugin\Validation\Constraint\UsernameFormatConstraint;
+use Drupal\do_username\Plugin\Validation\Constraint\UsernameFormatConstraintValidator;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\Validator\Context\ExecutionContextInterface;
+
+/**
+ * @coversDefaultClass \Drupal\do_username\Plugin\Validation\Constraint\UsernameFormatConstraintValidator
+ * @group do_username
+ */
+class UsernameFormatConstraintValidatorTest extends UnitTestCase {
+
+  /**
+   * @covers ::validate
+   *
+   * @dataProvider providerTestValidate
+   */
+  public function testValidate($item, $expected_violation) {
+    $constraint = new UsernameFormatConstraint();
+
+    // If a violation is expected, then the context's addViolation method will
+    // be called, otherwise it should not be called.
+    $context = $this->prophesize(ExecutionContextInterface::class);
+
+    if ($expected_violation) {
+      $context->addViolation()->shouldBeCalledTimes(1);
+    }
+    else {
+      $context->addViolation()->shouldNotBeCalled();
+    }
+
+    $validator = new UsernameFormatConstraintValidator();
+    $validator->initialize($context->reveal());
+    $validator->validate($item, $constraint);
+  }
+
+  /**
+   * Data provider for ::testValidate().
+   */
+  public function providerTestValidate() {
+    $cases = [];
+
+    $item = $this->prophesize(DrupalOrgUsernameItem::class);
+    $item->getValue()->willReturn(['value' => 'hussainweb']);
+    $cases['Valid Username'] = [$item, FALSE];
+
+    $item = $this->prophesize(DrupalOrgUsernameItem::class);
+    $item->getValue()->willReturn(['value' => ' hussainweb']);
+    $cases['Username beginning with space'] = [$item, TRUE];
+
+    $item = $this->prophesize(DrupalOrgUsernameItem::class);
+    $item->getValue()->willReturn(['value' => 'hussainweb ']);
+    $cases['Username ending with space'] = [$item, TRUE];
+
+    $item = $this->prophesize(DrupalOrgUsernameItem::class);
+    $item->getValue()->willReturn(['value' => 'hussain  web']);
+    $cases['Username with multiple spaces'] = [$item, TRUE];
+
+    $item = $this->prophesize(DrupalOrgUsernameItem::class);
+    $item->getValue()->willReturn(['value' => 'hussain[web]']);
+    $cases['Username with illegal characters'] = [$item, TRUE];
+
+    return $cases;
+  }
+
+}