diff --git a/tests/unit/Form/Util/StylesTest.php b/tests/unit/Form/Util/StylesTest.php
index 1a85b854b1..be7886534e 100644
--- a/tests/unit/Form/Util/StylesTest.php
+++ b/tests/unit/Form/Util/StylesTest.php
@@ -6,7 +6,6 @@ use MailPoet\Form\Util\Styles;
 
 class StylesTest extends \MailPoetUnitTest {
   function testItSetsDefaultCSSStyles() {
-    expect(property_exists('MailPoet\Form\Util\Styles', 'default_styles'))->true();
     expect(Styles::$default_styles)->notEmpty();
   }
 
@@ -25,4 +24,4 @@ class StylesTest extends \MailPoetUnitTest {
     . "mailpoet .another_style { font-size: 20px; }";
     expect($extracted_and_prefixed_styles)->equals($expected_result);
   }
-}
\ No newline at end of file
+}
diff --git a/tests/unit/Logging/LoggerFactoryTest.php b/tests/unit/Logging/LoggerFactoryTest.php
index 2ca1853a29..b2a92d4ad6 100644
--- a/tests/unit/Logging/LoggerFactoryTest.php
+++ b/tests/unit/Logging/LoggerFactoryTest.php
@@ -3,6 +3,7 @@
 namespace MailPoet\Logging;
 
 use MailPoet\Settings\SettingsController;
+use MailPoetVendor\Monolog\Handler\AbstractHandler;
 use PHPUnit_Framework_MockObject_MockObject as MockObject;
 
 class LoggerFactoryTest extends \MailPoetUnitTest {
@@ -53,6 +54,7 @@ class LoggerFactoryTest extends \MailPoetUnitTest {
     $this->settings->expects($this->once())->method('get')->willReturn(null);
     $logger1 = $this->logger_factory->getLogger('logger-with-handler');
     $handlers = $logger1->getHandlers();
+    assert($handlers[0] instanceof AbstractHandler);
     expect($handlers[0]->getLevel())->equals(\MailPoetVendor\Monolog\Logger::ERROR);
   }
 
@@ -60,6 +62,7 @@ class LoggerFactoryTest extends \MailPoetUnitTest {
     $this->settings->expects($this->once())->method('get')->willReturn('nothing');
     $logger1 = $this->logger_factory->getLogger('logger-for-nothing');
     $handlers = $logger1->getHandlers();
+    assert($handlers[0] instanceof AbstractHandler);
     expect($handlers[0]->getLevel())->equals(\MailPoetVendor\Monolog\Logger::EMERGENCY);
   }
 
@@ -67,6 +70,7 @@ class LoggerFactoryTest extends \MailPoetUnitTest {
     $this->settings->expects($this->once())->method('get')->willReturn('errors');
     $logger1 = $this->logger_factory->getLogger('logger-for-errors');
     $handlers = $logger1->getHandlers();
+    assert($handlers[0] instanceof AbstractHandler);
     expect($handlers[0]->getLevel())->equals(\MailPoetVendor\Monolog\Logger::ERROR);
   }
 
@@ -74,6 +78,7 @@ class LoggerFactoryTest extends \MailPoetUnitTest {
     $this->settings->expects($this->once())->method('get')->willReturn('everything');
     $logger1 = $this->logger_factory->getLogger('logger-for-everything');
     $handlers = $logger1->getHandlers();
+    assert($handlers[0] instanceof AbstractHandler);
     expect($handlers[0]->getLevel())->equals(\MailPoetVendor\Monolog\Logger::DEBUG);
   }
 }
diff --git a/tests/unit/Newsletter/Editor/StructureTransformerTest.php b/tests/unit/Newsletter/Editor/StructureTransformerTest.php
index 3794fafe5a..fb6864b8f2 100644
--- a/tests/unit/Newsletter/Editor/StructureTransformerTest.php
+++ b/tests/unit/Newsletter/Editor/StructureTransformerTest.php
@@ -5,6 +5,8 @@ namespace MailPoet\Test\Newsletter\Editor;
 use MailPoet\Newsletter\Editor\StructureTransformer;
 
 class StructureTransformerTest extends \MailPoetUnitTest {
+  /** @var StructureTransformer */
+  private $transformer;
 
   function _before() {
     parent::_before();
diff --git a/tests/unit/Newsletter/Renderer/Blocks/SocialTest.php b/tests/unit/Newsletter/Renderer/Blocks/SocialTest.php
index 48eb623ff4..bf3f4b80d6 100644
--- a/tests/unit/Newsletter/Renderer/Blocks/SocialTest.php
+++ b/tests/unit/Newsletter/Renderer/Blocks/SocialTest.php
@@ -35,7 +35,7 @@ class SocialTest extends \MailPoetUnitTest {
   ];
 
   function testItRendersCorrectly() {
-    $output = Social::render($this->block, 200);
+    $output = Social::render($this->block);
     $expected_result = '
       <tr>
         <td class="mailpoet_padded_side mailpoet_padded_vertical" valign="top" align="center">
diff --git a/tests/unit/Newsletter/Renderer/Blocks/TextTest.php b/tests/unit/Newsletter/Renderer/Blocks/TextTest.php
index 6999eaa6ae..11a408d98a 100644
--- a/tests/unit/Newsletter/Renderer/Blocks/TextTest.php
+++ b/tests/unit/Newsletter/Renderer/Blocks/TextTest.php
@@ -33,7 +33,9 @@ class TextTest extends \MailPoetUnitTest {
   function testItRendersParagraph() {
     $this->block['text'] = '<p>Text</p>';
     $output = Text::render($this->block);
-    $paragraph_table = $this->parser->parseStr($output)->query('table')[0]->toString();
+    $table = $this->parser->parseStr($output)->query('table');
+    assert($table instanceof \pQuery);
+    $paragraph_table = $table[0]->toString();
     $expected_result = '<table style="border-spacing:0;mso-table-lspace:0;mso-table-rspace:0;" width="100%" cellpadding="0">
         <tr>
           <td class="mailpoet_paragraph" style="word-break:break-word;word-wrap:break-word;text-align: left;">
@@ -46,7 +48,9 @@ class TextTest extends \MailPoetUnitTest {
   function testItRendersList() {
     $this->block['text'] = '<ul><li>Item 1</li><li>Item 2</li></ul>';
     $output = Text::render($this->block);
-    $list = $this->parser->parseStr($output)->query('ul')[0]->toString();
+    $ul = $this->parser->parseStr($output)->query('ul');
+    assert($ul instanceof \pQuery);
+    $list = $ul[0]->toString();
     $expected_result = '<ul class="mailpoet_paragraph" style="padding-top:0;padding-bottom:0;margin-top:10px;text-align:left;margin-bottom:10px;"><li class="mailpoet_paragraph" style="text-align:left;margin-bottom:10px;">Item 1</li><li class="mailpoet_paragraph" style="text-align:left;margin-bottom:10px;">Item 2</li></ul>';
     expect($list)->equals($expected_result);
   }
@@ -54,7 +58,9 @@ class TextTest extends \MailPoetUnitTest {
   function testItRendersBlockquotes() {
     $this->block['text'] = '<blockquote><p>Quote</p></blockquote>';
     $output = Text::render($this->block);
-    $blockquote_table = $this->parser->parseStr($output)->query('table')[0]->toString();
+    $table = $this->parser->parseStr($output)->query('table');
+    assert($table instanceof \pQuery);
+    $blockquote_table = $table[0]->toString();
     $expected_result = '<table class="mailpoet_blockquote" width="100%" spacing="0" border="0" cellpadding="0">
         <tbody>
           <tr>
diff --git a/tests/unit/Referrals/ReferralDetectorTest.php b/tests/unit/Referrals/ReferralDetectorTest.php
index 8d3aaa19ee..e72279b00a 100644
--- a/tests/unit/Referrals/ReferralDetectorTest.php
+++ b/tests/unit/Referrals/ReferralDetectorTest.php
@@ -8,10 +8,10 @@ use PHPUnit_Framework_MockObject_MockObject as MockObject;
 
 class ReferralDetectorTest extends \MailPoetUnitTest {
 
-  /** @var MockObject */
+  /** @var SettingsController&MockObject */
   private $settings_mock;
 
-  /** @var MockObject */
+  /** @var WPFunctions&MockObject */
   private $wp_mock;
 
   function _before() {
diff --git a/tests/unit/Subscribers/ImportExport/Import/MailChimpTest.php b/tests/unit/Subscribers/ImportExport/Import/MailChimpTest.php
index 1f30861616..92309d4a75 100644
--- a/tests/unit/Subscribers/ImportExport/Import/MailChimpTest.php
+++ b/tests/unit/Subscribers/ImportExport/Import/MailChimpTest.php
@@ -7,6 +7,15 @@ use MailPoet\Subscribers\ImportExport\Import\MailChimp;
 use MailPoet\WP\Functions as WPFunctions;
 
 class MailChimpTest extends \MailPoetUnitTest {
+  /** @var string */
+  private $api_key;
+
+  /** @var MailChimp */
+  private $mailchimp;
+
+  /** @var array */
+  private $lists;
+
   function __construct() {
     parent::__construct();
     $this->api_key = getenv('WP_TEST_IMPORT_MAILCHIMP_API');
diff --git a/tests/unit/Util/DOMTest.php b/tests/unit/Util/DOMTest.php
index 72b932a5fe..ef9f67e237 100644
--- a/tests/unit/Util/DOMTest.php
+++ b/tests/unit/Util/DOMTest.php
@@ -6,13 +6,17 @@ use MailPoet\Util\DOM as DOMUtil;
 use pQuery;
 
 class DOMTest extends \MailPoetUnitTest {
+  /** @var pQuery\DomNode */
+  private $root;
 
   function _before() {
     $this->root = pQuery::parseStr('<p><i>italic</i><em>previous text<a href="#mylink"><img src="#myimage" /></a>next text</em><b>bolded</b></p>');
   }
 
   function testItDeepSplitsDOMTreeByElement() {
-    DOMUtil::splitOn($this->root, $this->root->query('a')->offsetGet(0));
+    $a = $this->root->query('a');
+    assert($a instanceof pQuery);
+    DOMUtil::splitOn($this->root, $a->offsetGet(0));
 
     expect($this->root->html())->equals(
       '<p><i>italic</i><em>previous text</em></p>' .
@@ -22,8 +26,13 @@ class DOMTest extends \MailPoetUnitTest {
   }
 
   function testItFindsTopAncestor() {
-    $image = $this->root->query('img')->offsetGet(0);
-    $paragraph = $this->root->query('p')->offsetGet(0);
+    $img = $this->root->query('img');
+    assert($img instanceof pQuery);
+    $image = $img->offsetGet(0);
+
+    $p = $this->root->query('p');
+    assert($p instanceof pQuery);
+    $paragraph = $p->offsetGet(0);
 
     expect(DOMUtil::findTopAncestor($image))->equals($paragraph);
   }
diff --git a/tests/unit/WP/ReadmeTest.php b/tests/unit/WP/ReadmeTest.php
index cdab1a5887..ae469602d8 100644
--- a/tests/unit/WP/ReadmeTest.php
+++ b/tests/unit/WP/ReadmeTest.php
@@ -5,6 +5,9 @@ namespace MailPoet\Test\WP;
 use MailPoet\WP\Readme;
 
 class ReadmeTest extends \MailPoetUnitTest {
+  /** @var string */
+  private $data;
+
   function _before() {
     // Sample taken from https://wordpress.org/plugins/about/readme.txt
     $this->data = file_get_contents(dirname(__FILE__) . '/ReadmeTestData.txt');