diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 103e745..f1065f9 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -21,11 +21,6 @@ jobs:
           - windows-latest
 
         php:
-          - "5.6"
-          - "7.0"
-          - "7.1"
-          - "7.2"
-          - "7.3"
           - "7.4"
           - "8.0"
           - "8.1"
diff --git a/composer.json b/composer.json
index e3068b0..7db83cf 100644
--- a/composer.json
+++ b/composer.json
@@ -14,24 +14,27 @@
     },
     "minimum-stability": "dev",
     "require": {
-        "php": ">=5.6.0",
+        "php": ">=7.4.0",
         "yiisoft/yii2": "~2.0.14",
         "yiisoft/yii2-bootstrap4": "~2.0.0",
-        "yiisoft/yii2-swiftmailer": "~2.0.0 || ~2.1.0"
+        "yiisoft/yii2-swiftmailer": "~2.0.0 || ~2.1.0",
+        "yiisoft/yii2-symfonymailer": "~2.0.3"
     },
     "require-dev": {
         "yiisoft/yii2-debug": "~2.1.0",
         "yiisoft/yii2-gii": "~2.2.0",
         "yiisoft/yii2-faker": "~2.0.0",
         "codeception/codeception": "^4.0",
-        "codeception/verify": "~0.5.0 || ~1.1.0",
-        "codeception/specify": "~0.4.6",
-        "symfony/browser-kit": ">=2.7 <=4.2.4",
-        "codeception/module-filesystem": "^1.0.0",
-        "codeception/module-yii2": "^1.0.0",
-        "codeception/module-asserts": "^1.0.0"
+        "codeception/module-asserts": "^1.0",
+        "codeception/module-yii2": "^1.0",
+        "codeception/module-filesystem": "^1.0",
+        "codeception/verify": "^2.2",
+        "symfony/browser-kit": ">=2.7 <=4.2.4"
     },
     "config": {
+        "allow-plugins": {
+            "yiisoft/yii2-composer" : true
+        },
         "process-timeout": 1800,
         "fxp-asset": {
             "enabled": false
diff --git a/controllers/SiteController.php b/controllers/SiteController.php
index 6e8a85d..67c3f50 100644
--- a/controllers/SiteController.php
+++ b/controllers/SiteController.php
@@ -19,7 +19,7 @@ class SiteController extends Controller
     {
         return [
             'access' => [
-                'class' => AccessControl::className(),
+                'class' => AccessControl::class,
                 'only' => ['logout'],
                 'rules' => [
                     [
@@ -30,7 +30,7 @@ class SiteController extends Controller
                 ],
             ],
             'verbs' => [
-                'class' => VerbFilter::className(),
+                'class' => VerbFilter::class,
                 'actions' => [
                     'logout' => ['post'],
                 ],
diff --git a/tests/unit/models/ContactFormTest.php b/tests/unit/models/ContactFormTest.php
index 93313e4..1bb1bb2 100644
--- a/tests/unit/models/ContactFormTest.php
+++ b/tests/unit/models/ContactFormTest.php
@@ -24,18 +24,18 @@ class ContactFormTest extends \Codeception\Test\Unit
             'verifyCode' => 'testme',
         ];
 
-        expect_that($model->contact('admin@example.com'));
+        verify($model->contact('admin@example.com'))->notEmpty();
 
         // using Yii2 module actions to check email was sent
         $this->tester->seeEmailIsSent();
 
         /** @var MessageInterface $emailMessage */
         $emailMessage = $this->tester->grabLastSentEmail();
-        expect('valid email is sent', $emailMessage)->isInstanceOf('yii\mail\MessageInterface');
-        expect($emailMessage->getTo())->hasKey('admin@example.com');
-        expect($emailMessage->getFrom())->hasKey('noreply@example.com');
-        expect($emailMessage->getReplyTo())->hasKey('tester@example.com');
-        expect($emailMessage->getSubject())->equals('very important letter subject');
-        expect($emailMessage->toString())->stringContainsString('body of current message');
+        verify($emailMessage)->instanceOf('yii\mail\MessageInterface');
+        verify($emailMessage->getTo())->arrayHasKey('admin@example.com');
+        verify($emailMessage->getFrom())->arrayHasKey('noreply@example.com');
+        verify($emailMessage->getReplyTo())->arrayHasKey('tester@example.com');
+        verify($emailMessage->getSubject())->equals('very important letter subject');
+        verify($emailMessage->toString())->stringContainsString('body of current message');
     }
 }
diff --git a/tests/unit/models/LoginFormTest.php b/tests/unit/models/LoginFormTest.php
index ecdb145..3c1dcdd 100644
--- a/tests/unit/models/LoginFormTest.php
+++ b/tests/unit/models/LoginFormTest.php
@@ -20,8 +20,8 @@ class LoginFormTest extends \Codeception\Test\Unit
             'password' => 'not_existing_password',
         ]);
 
-        expect_not($this->model->login());
-        expect_that(\Yii::$app->user->isGuest);
+        verify($this->model->login())->false();
+        verify(\Yii::$app->user->isGuest)->true();
     }
 
     public function testLoginWrongPassword()
@@ -31,9 +31,9 @@ class LoginFormTest extends \Codeception\Test\Unit
             'password' => 'wrong_password',
         ]);
 
-        expect_not($this->model->login());
-        expect_that(\Yii::$app->user->isGuest);
-        expect($this->model->errors)->hasKey('password');
+        verify($this->model->login())->false();
+        verify(\Yii::$app->user->isGuest)->true();
+        verify($this->model->errors)->arrayHasKey('password');
     }
 
     public function testLoginCorrect()
@@ -43,9 +43,9 @@ class LoginFormTest extends \Codeception\Test\Unit
             'password' => 'demo',
         ]);
 
-        expect_that($this->model->login());
-        expect_not(\Yii::$app->user->isGuest);
-        expect($this->model->errors)->hasntKey('password');
+        verify($this->model->login())->true();
+        verify(\Yii::$app->user->isGuest)->false();
+        verify($this->model->errors)->arrayHasNotKey('password');
     }
 
 }
diff --git a/tests/unit/models/UserTest.php b/tests/unit/models/UserTest.php
index cb61278..cd10725 100644
--- a/tests/unit/models/UserTest.php
+++ b/tests/unit/models/UserTest.php
@@ -8,24 +8,24 @@ class UserTest extends \Codeception\Test\Unit
 {
     public function testFindUserById()
     {
-        expect_that($user = User::findIdentity(100));
-        expect($user->username)->equals('admin');
+        verify($user = User::findIdentity(100))->notEmpty();
+        verify($user->username)->equals('admin');
 
-        expect_not(User::findIdentity(999));
+        verify(User::findIdentity(999))->empty();
     }
 
     public function testFindUserByAccessToken()
     {
-        expect_that($user = User::findIdentityByAccessToken('100-token'));
-        expect($user->username)->equals('admin');
+        verify($user = User::findIdentityByAccessToken('100-token'))->notEmpty();
+        verify($user->username)->equals('admin');
 
-        expect_not(User::findIdentityByAccessToken('non-existing'));        
+        verify(User::findIdentityByAccessToken('non-existing'))->empty();        
     }
 
     public function testFindUserByUsername()
     {
-        expect_that($user = User::findByUsername('admin'));
-        expect_not(User::findByUsername('not-admin'));
+        verify($user = User::findByUsername('admin'))->notEmpty();
+        verify(User::findByUsername('not-admin'))->empty();
     }
 
     /**
@@ -34,11 +34,11 @@ class UserTest extends \Codeception\Test\Unit
     public function testValidateUser($user)
     {
         $user = User::findByUsername('admin');
-        expect_that($user->validateAuthKey('test100key'));
-        expect_not($user->validateAuthKey('test102key'));
+        verify($user->validateAuthKey('test100key'))->notEmpty();
+        verify($user->validateAuthKey('test102key'))->empty();
 
-        expect_that($user->validatePassword('admin'));
-        expect_not($user->validatePassword('123456'));        
+        verify($user->validatePassword('admin'))->notEmpty();
+        verify($user->validatePassword('123456'))->empty();        
     }
 
 }
diff --git a/tests/unit/widgets/AlertTest.php b/tests/unit/widgets/AlertTest.php
index 5a84cbd..e9857a1 100644
--- a/tests/unit/widgets/AlertTest.php
+++ b/tests/unit/widgets/AlertTest.php
@@ -15,12 +15,12 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($message);
-        expect($renderingResult)->stringContainsString('alert-danger');
+        verify($renderingResult)->stringContainsString($message);
+        verify($renderingResult)->stringContainsString('alert-danger');
 
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-info');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testMultipleErrorMessages()
@@ -32,13 +32,13 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($firstMessage);
-        expect($renderingResult)->stringContainsString($secondMessage);
-        expect($renderingResult)->stringContainsString('alert-danger');
+        verify($renderingResult)->stringContainsString($firstMessage);
+        verify($renderingResult)->stringContainsString($secondMessage);
+        verify($renderingResult)->stringContainsString('alert-danger');
 
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-info');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testSingleDangerMessage()
@@ -49,12 +49,12 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($message);
-        expect($renderingResult)->stringContainsString('alert-danger');
+        verify($renderingResult)->stringContainsString($message);
+        verify($renderingResult)->stringContainsString('alert-danger');
 
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-info');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testMultipleDangerMessages()
@@ -66,13 +66,13 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($firstMessage);
-        expect($renderingResult)->stringContainsString($secondMessage);
-        expect($renderingResult)->stringContainsString('alert-danger');
+        verify($renderingResult)->stringContainsString($firstMessage);
+        verify($renderingResult)->stringContainsString($secondMessage);
+        verify($renderingResult)->stringContainsString('alert-danger');
 
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-info');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testSingleSuccessMessage()
@@ -83,12 +83,12 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($message);
-        expect($renderingResult)->stringContainsString('alert-success');
+        verify($renderingResult)->stringContainsString($message);
+        verify($renderingResult)->stringContainsString('alert-success');
 
-        expect($renderingResult)->stringNotContainsString('alert-danger');
-        expect($renderingResult)->stringNotContainsString('alert-info');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-danger');
+        verify($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testMultipleSuccessMessages()
@@ -100,13 +100,13 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($firstMessage);
-        expect($renderingResult)->stringContainsString($secondMessage);
-        expect($renderingResult)->stringContainsString('alert-success');
+        verify($renderingResult)->stringContainsString($firstMessage);
+        verify($renderingResult)->stringContainsString($secondMessage);
+        verify($renderingResult)->stringContainsString('alert-success');
 
-        expect($renderingResult)->stringNotContainsString('alert-danger');
-        expect($renderingResult)->stringNotContainsString('alert-info');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-danger');
+        verify($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testSingleInfoMessage()
@@ -117,12 +117,12 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($message);
-        expect($renderingResult)->stringContainsString('alert-info');
+        verify($renderingResult)->stringContainsString($message);
+        verify($renderingResult)->stringContainsString('alert-info');
 
-        expect($renderingResult)->stringNotContainsString('alert-danger');
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-danger');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testMultipleInfoMessages()
@@ -134,13 +134,13 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($firstMessage);
-        expect($renderingResult)->stringContainsString($secondMessage);
-        expect($renderingResult)->stringContainsString('alert-info');
+        verify($renderingResult)->stringContainsString($firstMessage);
+        verify($renderingResult)->stringContainsString($secondMessage);
+        verify($renderingResult)->stringContainsString('alert-info');
 
-        expect($renderingResult)->stringNotContainsString('alert-danger');
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-warning');
+        verify($renderingResult)->stringNotContainsString('alert-danger');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-warning');
     }
 
     public function testSingleWarningMessage()
@@ -151,12 +151,12 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($message);
-        expect($renderingResult)->stringContainsString('alert-warning');
+        verify($renderingResult)->stringContainsString($message);
+        verify($renderingResult)->stringContainsString('alert-warning');
 
-        expect($renderingResult)->stringNotContainsString('alert-danger');
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-danger');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-info');
     }
 
     public function testMultipleWarningMessages()
@@ -168,13 +168,13 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($firstMessage);
-        expect($renderingResult)->stringContainsString($secondMessage);
-        expect($renderingResult)->stringContainsString('alert-warning');
+        verify($renderingResult)->stringContainsString($firstMessage);
+        verify($renderingResult)->stringContainsString($secondMessage);
+        verify($renderingResult)->stringContainsString('alert-warning');
 
-        expect($renderingResult)->stringNotContainsString('alert-danger');
-        expect($renderingResult)->stringNotContainsString('alert-success');
-        expect($renderingResult)->stringNotContainsString('alert-info');
+        verify($renderingResult)->stringNotContainsString('alert-danger');
+        verify($renderingResult)->stringNotContainsString('alert-success');
+        verify($renderingResult)->stringNotContainsString('alert-info');
     }
 
     public function testSingleMixedMessages() {
@@ -192,16 +192,16 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($errorMessage);
-        expect($renderingResult)->stringContainsString($dangerMessage);
-        expect($renderingResult)->stringContainsString($successMessage);
-        expect($renderingResult)->stringContainsString($infoMessage);
-        expect($renderingResult)->stringContainsString($warningMessage);
+        verify($renderingResult)->stringContainsString($errorMessage);
+        verify($renderingResult)->stringContainsString($dangerMessage);
+        verify($renderingResult)->stringContainsString($successMessage);
+        verify($renderingResult)->stringContainsString($infoMessage);
+        verify($renderingResult)->stringContainsString($warningMessage);
 
-        expect($renderingResult)->stringContainsString('alert-danger');
-        expect($renderingResult)->stringContainsString('alert-success');
-        expect($renderingResult)->stringContainsString('alert-info');
-        expect($renderingResult)->stringContainsString('alert-warning');
+        verify($renderingResult)->stringContainsString('alert-danger');
+        verify($renderingResult)->stringContainsString('alert-success');
+        verify($renderingResult)->stringContainsString('alert-info');
+        verify($renderingResult)->stringContainsString('alert-warning');
     }
 
     public function testMultipleMixedMessages() {
@@ -224,21 +224,21 @@ class AlertTest extends \Codeception\Test\Unit
 
         $renderingResult = Alert::widget();
 
-        expect($renderingResult)->stringContainsString($firstErrorMessage);
-        expect($renderingResult)->stringContainsString($secondErrorMessage);
-        expect($renderingResult)->stringContainsString($firstDangerMessage);
-        expect($renderingResult)->stringContainsString($secondDangerMessage);
-        expect($renderingResult)->stringContainsString($firstSuccessMessage);
-        expect($renderingResult)->stringContainsString($secondSuccessMessage);
-        expect($renderingResult)->stringContainsString($firstInfoMessage);
-        expect($renderingResult)->stringContainsString($secondInfoMessage);
-        expect($renderingResult)->stringContainsString($firstWarningMessage);
-        expect($renderingResult)->stringContainsString($secondWarningMessage);
+        verify($renderingResult)->stringContainsString($firstErrorMessage);
+        verify($renderingResult)->stringContainsString($secondErrorMessage);
+        verify($renderingResult)->stringContainsString($firstDangerMessage);
+        verify($renderingResult)->stringContainsString($secondDangerMessage);
+        verify($renderingResult)->stringContainsString($firstSuccessMessage);
+        verify($renderingResult)->stringContainsString($secondSuccessMessage);
+        verify($renderingResult)->stringContainsString($firstInfoMessage);
+        verify($renderingResult)->stringContainsString($secondInfoMessage);
+        verify($renderingResult)->stringContainsString($firstWarningMessage);
+        verify($renderingResult)->stringContainsString($secondWarningMessage);
 
-        expect($renderingResult)->stringContainsString('alert-danger');
-        expect($renderingResult)->stringContainsString('alert-success');
-        expect($renderingResult)->stringContainsString('alert-info');
-        expect($renderingResult)->stringContainsString('alert-warning');
+        verify($renderingResult)->stringContainsString('alert-danger');
+        verify($renderingResult)->stringContainsString('alert-success');
+        verify($renderingResult)->stringContainsString('alert-info');
+        verify($renderingResult)->stringContainsString('alert-warning');
     }
 
     public function testFlashIntegrity()
@@ -255,7 +255,7 @@ class AlertTest extends \Codeception\Test\Unit
         Yii::$app->session->close();
         Yii::$app->session->open();
 
-        expect(Yii::$app->session->getFlash('error'))->null();
-        expect(Yii::$app->session->getFlash('unrelated'))->equals($unrelatedMessage);
+        verify(Yii::$app->session->getFlash('error'))->empty();
+        verify(Yii::$app->session->getFlash('unrelated'))->equals($unrelatedMessage);
     }
 }
diff --git a/views/site/contact.php b/views/site/contact.php
index d92e21f..4ae25a9 100644
--- a/views/site/contact.php
+++ b/views/site/contact.php
@@ -51,7 +51,7 @@ $this->params['breadcrumbs'][] = $this->title;
 
                     <?= $form->field($model, 'body')->textarea(['rows' => 6]) ?>
 
-                    <?= $form->field($model, 'verifyCode')->widget(Captcha::className(), [
+                    <?= $form->field($model, 'verifyCode')->widget(Captcha::class, [
                         'template' => '<div class="row"><div class="col-lg-3">{image}</div><div class="col-lg-6">{input}</div></div>',
                     ]) ?>