diff --git a/src/Iterators/CachingIterator.php b/src/Iterators/CachingIterator.php
index 0c5538e96..0de5ca11b 100644
--- a/src/Iterators/CachingIterator.php
+++ b/src/Iterators/CachingIterator.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Iterators;
 
 use Nette;
diff --git a/src/Iterators/Mapper.php b/src/Iterators/Mapper.php
index f52e40264..6b992a3de 100644
--- a/src/Iterators/Mapper.php
+++ b/src/Iterators/Mapper.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Iterators;
 
 use Nette;
diff --git a/src/Utils/ArrayHash.php b/src/Utils/ArrayHash.php
index fa7699f24..27b9fbc4c 100644
--- a/src/Utils/ArrayHash.php
+++ b/src/Utils/ArrayHash.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/ArrayList.php b/src/Utils/ArrayList.php
index 580fbe4d2..5c1f3d11b 100644
--- a/src/Utils/ArrayList.php
+++ b/src/Utils/ArrayList.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Arrays.php b/src/Utils/Arrays.php
index 8140c3f18..cb2a4c505 100644
--- a/src/Utils/Arrays.php
+++ b/src/Utils/Arrays.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Callback.php b/src/Utils/Callback.php
index 3db1abac0..c5d73dce9 100644
--- a/src/Utils/Callback.php
+++ b/src/Utils/Callback.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/DateTime.php b/src/Utils/DateTime.php
index 51748c7f3..cb0202678 100644
--- a/src/Utils/DateTime.php
+++ b/src/Utils/DateTime.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/FileSystem.php b/src/Utils/FileSystem.php
index 5402d0fc8..ae9937a54 100644
--- a/src/Utils/FileSystem.php
+++ b/src/Utils/FileSystem.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Html.php b/src/Utils/Html.php
index 7c38e4849..238b7616a 100644
--- a/src/Utils/Html.php
+++ b/src/Utils/Html.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/IHtmlString.php b/src/Utils/IHtmlString.php
index 71e44ca94..cd281e6c6 100644
--- a/src/Utils/IHtmlString.php
+++ b/src/Utils/IHtmlString.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 
diff --git a/src/Utils/ITranslator.php b/src/Utils/ITranslator.php
index 6c62415e6..619e7b8f2 100644
--- a/src/Utils/ITranslator.php
+++ b/src/Utils/ITranslator.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Localization;
 
 
diff --git a/src/Utils/Image.php b/src/Utils/Image.php
index b5320d568..cbe75aec9 100644
--- a/src/Utils/Image.php
+++ b/src/Utils/Image.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Json.php b/src/Utils/Json.php
index d2dfaf16b..ffd8ec65f 100644
--- a/src/Utils/Json.php
+++ b/src/Utils/Json.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Object.php b/src/Utils/Object.php
index 505d65706..4a7f7c9b4 100644
--- a/src/Utils/Object.php
+++ b/src/Utils/Object.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette;
 
 use Nette;
diff --git a/src/Utils/ObjectMixin.php b/src/Utils/ObjectMixin.php
index bed2ee657..cc0c215a9 100644
--- a/src/Utils/ObjectMixin.php
+++ b/src/Utils/ObjectMixin.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Paginator.php b/src/Utils/Paginator.php
index 1f72dcc37..ba43264dc 100644
--- a/src/Utils/Paginator.php
+++ b/src/Utils/Paginator.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Random.php b/src/Utils/Random.php
index b5bcca3ad..b260c55c4 100644
--- a/src/Utils/Random.php
+++ b/src/Utils/Random.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Reflection.php b/src/Utils/Reflection.php
index 8df516fd1..131aad282 100644
--- a/src/Utils/Reflection.php
+++ b/src/Utils/Reflection.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/SmartObject.php b/src/Utils/SmartObject.php
index e7ba7b52a..e1ebcc3b6 100644
--- a/src/Utils/SmartObject.php
+++ b/src/Utils/SmartObject.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette;
 
 use Nette\Utils\Callback;
diff --git a/src/Utils/StaticClass.php b/src/Utils/StaticClass.php
index b5f7b9400..7e9e5298b 100644
--- a/src/Utils/StaticClass.php
+++ b/src/Utils/StaticClass.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette;
 
 
diff --git a/src/Utils/Strings.php b/src/Utils/Strings.php
index bb43bc207..2c2948e2d 100644
--- a/src/Utils/Strings.php
+++ b/src/Utils/Strings.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/Validators.php b/src/Utils/Validators.php
index e3c2aeeda..d84cec456 100644
--- a/src/Utils/Validators.php
+++ b/src/Utils/Validators.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette\Utils;
 
 use Nette;
diff --git a/src/Utils/exceptions.php b/src/Utils/exceptions.php
index 0b759ff06..f7af9b4ef 100644
--- a/src/Utils/exceptions.php
+++ b/src/Utils/exceptions.php
@@ -5,6 +5,8 @@
  * Copyright (c) 2004 David Grudl (https://davidgrudl.com)
  */
 
+declare(strict_types=1);
+
 namespace Nette;
 
 
diff --git a/tests/Iterators/CachingIterator.basic.phpt b/tests/Iterators/CachingIterator.basic.phpt
index dd2a09bb8..c407af7a2 100644
--- a/tests/Iterators/CachingIterator.basic.phpt
+++ b/tests/Iterators/CachingIterator.basic.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Iterators\CachingIterator basic usage.
  */
 
+declare(strict_types=1);
+
 use Nette\Iterators;
 use Tester\Assert;
 
diff --git a/tests/Iterators/CachingIterator.construct.phpt b/tests/Iterators/CachingIterator.construct.phpt
index 3412b6425..8e202c09d 100644
--- a/tests/Iterators/CachingIterator.construct.phpt
+++ b/tests/Iterators/CachingIterator.construct.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Iterators\CachingIterator constructor.
  */
 
+declare(strict_types=1);
+
 use Nette\Iterators;
 use Tester\Assert;
 
diff --git a/tests/Iterators/CachingIterator.width.phpt b/tests/Iterators/CachingIterator.width.phpt
index 4bf6c0320..37308feda 100644
--- a/tests/Iterators/CachingIterator.width.phpt
+++ b/tests/Iterators/CachingIterator.width.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Iterators\CachingIterator width.
  */
 
+declare(strict_types=1);
+
 use Nette\Iterators;
 use Tester\Assert;
 
diff --git a/tests/Iterators/Mapper.phpt b/tests/Iterators/Mapper.phpt
index 34458572a..6d429360b 100644
--- a/tests/Iterators/Mapper.phpt
+++ b/tests/Iterators/Mapper.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Iterators\Mapper
  */
 
+declare(strict_types=1);
+
 use Nette\Iterators;
 use Tester\Assert;
 
diff --git a/tests/Utils/ArrayHash.phpt b/tests/Utils/ArrayHash.phpt
index 597b936d9..e715aad29 100644
--- a/tests/Utils/ArrayHash.phpt
+++ b/tests/Utils/ArrayHash.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\ArrayHash basic usage.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\ArrayHash;
 use Tester\Assert;
 
diff --git a/tests/Utils/ArrayList.phpt b/tests/Utils/ArrayList.phpt
index 4969b8c6b..28d0e18f1 100644
--- a/tests/Utils/ArrayList.phpt
+++ b/tests/Utils/ArrayList.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\ArrayList basic usage.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\ArrayList;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.associate().error.phpt b/tests/Utils/Arrays.associate().error.phpt
index d9a7cb542..b1b441772 100644
--- a/tests/Utils/Arrays.associate().error.phpt
+++ b/tests/Utils/Arrays.associate().error.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::associate()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.associate().phpt b/tests/Utils/Arrays.associate().phpt
index 8878c29b9..7612ddd65 100644
--- a/tests/Utils/Arrays.associate().phpt
+++ b/tests/Utils/Arrays.associate().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::associate()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Nette\Utils\DateTime;
 use Tester\Assert;
diff --git a/tests/Utils/Arrays.every().phpt b/tests/Utils/Arrays.every().phpt
index 3f959dca3..8d7203467 100644
--- a/tests/Utils/Arrays.every().phpt
+++ b/tests/Utils/Arrays.every().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::every()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.flatten().phpt b/tests/Utils/Arrays.flatten().phpt
index e73189dff..bc33f3155 100644
--- a/tests/Utils/Arrays.flatten().phpt
+++ b/tests/Utils/Arrays.flatten().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::flatten()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.get().phpt b/tests/Utils/Arrays.get().phpt
index 474c4c33c..41d55f220 100644
--- a/tests/Utils/Arrays.get().phpt
+++ b/tests/Utils/Arrays.get().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::get()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.getRef().phpt b/tests/Utils/Arrays.getRef().phpt
index d9097ed5c..e7ff59419 100644
--- a/tests/Utils/Arrays.getRef().phpt
+++ b/tests/Utils/Arrays.getRef().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::getRef()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.grep().errors.phpt b/tests/Utils/Arrays.grep().errors.phpt
index bd2203875..74697cbc3 100644
--- a/tests/Utils/Arrays.grep().errors.phpt
+++ b/tests/Utils/Arrays.grep().errors.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::grep() errors.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.grep().phpt b/tests/Utils/Arrays.grep().phpt
index c7576e580..f356405d3 100644
--- a/tests/Utils/Arrays.grep().phpt
+++ b/tests/Utils/Arrays.grep().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::grep()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.insertBefore().phpt b/tests/Utils/Arrays.insertBefore().phpt
index 03b52cbc8..7a2230c22 100644
--- a/tests/Utils/Arrays.insertBefore().phpt
+++ b/tests/Utils/Arrays.insertBefore().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::insertBefore() & insertAfter()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.isList.phpt b/tests/Utils/Arrays.isList.phpt
index 2b376cea6..24a73664a 100644
--- a/tests/Utils/Arrays.isList.phpt
+++ b/tests/Utils/Arrays.isList.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::isList()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.map().phpt b/tests/Utils/Arrays.map().phpt
index 4b11bf5c1..8b0d3395a 100644
--- a/tests/Utils/Arrays.map().phpt
+++ b/tests/Utils/Arrays.map().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::map()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.normalize.phpt b/tests/Utils/Arrays.normalize.phpt
index e80fde131..3988010f3 100644
--- a/tests/Utils/Arrays.normalize.phpt
+++ b/tests/Utils/Arrays.normalize.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::searchKey()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.pick().phpt b/tests/Utils/Arrays.pick().phpt
index ca7cce606..082ffb11c 100644
--- a/tests/Utils/Arrays.pick().phpt
+++ b/tests/Utils/Arrays.pick().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::pick()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.renameKey().phpt b/tests/Utils/Arrays.renameKey().phpt
index 01c479c1e..85651093f 100644
--- a/tests/Utils/Arrays.renameKey().phpt
+++ b/tests/Utils/Arrays.renameKey().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::renameKey()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.searchKey().phpt b/tests/Utils/Arrays.searchKey().phpt
index 13f701afa..f0d0ac723 100644
--- a/tests/Utils/Arrays.searchKey().phpt
+++ b/tests/Utils/Arrays.searchKey().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::searchKey()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Arrays.some().phpt b/tests/Utils/Arrays.some().phpt
index 7ec383951..b213c2fdb 100644
--- a/tests/Utils/Arrays.some().phpt
+++ b/tests/Utils/Arrays.some().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Arrays::some()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Arrays;
 use Tester\Assert;
 
diff --git a/tests/Utils/Callback.check.phpt b/tests/Utils/Callback.check.phpt
index 2e0766a1a..defa96f14 100644
--- a/tests/Utils/Callback.check.phpt
+++ b/tests/Utils/Callback.check.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Callback::check()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Callback;
 use Tester\Assert;
 
diff --git a/tests/Utils/Callback.closure.phpt b/tests/Utils/Callback.closure.phpt
index d361b4eb2..3dd9f8453 100644
--- a/tests/Utils/Callback.closure.phpt
+++ b/tests/Utils/Callback.closure.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Callback closures tests.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Callback;
 use Tester\Assert;
 
diff --git a/tests/Utils/Callback.invoke.phpt b/tests/Utils/Callback.invoke.phpt
index e3a5f3ecb..6b4c21436 100644
--- a/tests/Utils/Callback.invoke.phpt
+++ b/tests/Utils/Callback.invoke.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Callback::invoke() and invokeArgs()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Callback;
 use Tester\Assert;
 
diff --git a/tests/Utils/Callback.invokeSafe.phpt b/tests/Utils/Callback.invokeSafe.phpt
index 3d58b6f37..1518612c9 100644
--- a/tests/Utils/Callback.invokeSafe.phpt
+++ b/tests/Utils/Callback.invokeSafe.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Callback::invokeSafe()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Callback;
 use Tester\Assert;
 
diff --git a/tests/Utils/DateTime.JSON.phpt b/tests/Utils/DateTime.JSON.phpt
index eb57b297f..8fd9dafbb 100644
--- a/tests/Utils/DateTime.JSON.phpt
+++ b/tests/Utils/DateTime.JSON.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\DateTime & JSON.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 use Nette\Utils\DateTime;
 
diff --git a/tests/Utils/DateTime.createFromFormat.phpt b/tests/Utils/DateTime.createFromFormat.phpt
index c1a165887..2ae02822f 100644
--- a/tests/Utils/DateTime.createFromFormat.phpt
+++ b/tests/Utils/DateTime.createFromFormat.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\DateTime::createFromFormat().
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 use Nette\Utils\DateTime;
 
diff --git a/tests/Utils/DateTime.from.phpt b/tests/Utils/DateTime.from.phpt
index 0c806f6ea..ff8f31b19 100644
--- a/tests/Utils/DateTime.from.phpt
+++ b/tests/Utils/DateTime.from.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\DateTime::from().
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 use Nette\Utils\DateTime;
 
diff --git a/tests/Utils/DateTime.fromParts.phpt b/tests/Utils/DateTime.fromParts.phpt
index ffa40580a..7fe554667 100644
--- a/tests/Utils/DateTime.fromParts.phpt
+++ b/tests/Utils/DateTime.fromParts.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\DateTime::fromParts().
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 use Nette\Utils\DateTime;
 
diff --git a/tests/Utils/FileSystem.phpt b/tests/Utils/FileSystem.phpt
index 8e094f585..acf8c3757 100644
--- a/tests/Utils/FileSystem.phpt
+++ b/tests/Utils/FileSystem.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\FileSystem basic usage.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\FileSystem;
 use Tester\Assert;
 
diff --git a/tests/Utils/Html.basic.phpt b/tests/Utils/Html.basic.phpt
index 9517e9396..b9c8c3a92 100644
--- a/tests/Utils/Html.basic.phpt
+++ b/tests/Utils/Html.basic.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Html basic usage.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Html;
 use Tester\Assert;
 
diff --git a/tests/Utils/Html.children.phpt b/tests/Utils/Html.children.phpt
index b0dcb15ac..729325ae6 100644
--- a/tests/Utils/Html.children.phpt
+++ b/tests/Utils/Html.children.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Html children usage.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Html;
 use Tester\Assert;
 
diff --git a/tests/Utils/Html.construct.phpt b/tests/Utils/Html.construct.phpt
index cb93ab3be..949f5bc41 100644
--- a/tests/Utils/Html.construct.phpt
+++ b/tests/Utils/Html.construct.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Html::__construct()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Html;
 use Tester\Assert;
 
diff --git a/tests/Utils/Html.data.phpt b/tests/Utils/Html.data.phpt
index 8c097410d..f7fb18c7b 100644
--- a/tests/Utils/Html.data.phpt
+++ b/tests/Utils/Html.data.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Html user data attribute.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Html;
 use Tester\Assert;
 
diff --git a/tests/Utils/Html.style.phpt b/tests/Utils/Html.style.phpt
index 4b38c26f4..83ee22dac 100644
--- a/tests/Utils/Html.style.phpt
+++ b/tests/Utils/Html.style.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Html style & class attribute.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Html;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.alpha1.phpt b/tests/Utils/Image.alpha1.phpt
index b6a5b32f8..9a7094b48 100644
--- a/tests/Utils/Image.alpha1.phpt
+++ b/tests/Utils/Image.alpha1.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image alpha channel.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.alpha2.phpt b/tests/Utils/Image.alpha2.phpt
index 692fdca49..721b4ff86 100644
--- a/tests/Utils/Image.alpha2.phpt
+++ b/tests/Utils/Image.alpha2.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image alpha channel.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.clone.phpt b/tests/Utils/Image.clone.phpt
index 74e625e80..a562c08c5 100644
--- a/tests/Utils/Image.clone.phpt
+++ b/tests/Utils/Image.clone.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image cloning.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.drawing.phpt b/tests/Utils/Image.drawing.phpt
index a94441a1d..a74d44f86 100644
--- a/tests/Utils/Image.drawing.phpt
+++ b/tests/Utils/Image.drawing.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image drawing.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.factories.phpt b/tests/Utils/Image.factories.phpt
index 514e525a6..bd4d3dc05 100644
--- a/tests/Utils/Image.factories.phpt
+++ b/tests/Utils/Image.factories.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image factories.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.place.phpt b/tests/Utils/Image.place.phpt
index cd7f9bb34..9ea0389c2 100644
--- a/tests/Utils/Image.place.phpt
+++ b/tests/Utils/Image.place.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image place image.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.resize.phpt b/tests/Utils/Image.resize.phpt
index f1213a732..5f8ae3611 100644
--- a/tests/Utils/Image.resize.phpt
+++ b/tests/Utils/Image.resize.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image crop, resize & flip.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.save.phpt b/tests/Utils/Image.save.phpt
index ca61c4949..f5d6886ce 100644
--- a/tests/Utils/Image.save.phpt
+++ b/tests/Utils/Image.save.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image save method exceptions.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Image.send.phpt b/tests/Utils/Image.send.phpt
index 6b8e00850..8beda17b3 100644
--- a/tests/Utils/Image.send.phpt
+++ b/tests/Utils/Image.send.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Image send method exceptions.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Image;
 use Tester\Assert;
 
diff --git a/tests/Utils/Json.decode().phpt b/tests/Utils/Json.decode().phpt
index 1eb27b154..5b654311f 100644
--- a/tests/Utils/Json.decode().phpt
+++ b/tests/Utils/Json.decode().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Json::decode()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Json;
 use Tester\Assert;
 
diff --git a/tests/Utils/Json.encode().phpt b/tests/Utils/Json.encode().phpt
index 8b2e4ebaf..c469afa3d 100644
--- a/tests/Utils/Json.encode().phpt
+++ b/tests/Utils/Json.encode().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Json::encode()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Json;
 use Tester\Assert;
 
diff --git a/tests/Utils/Object.arrayProperty.phpt b/tests/Utils/Object.arrayProperty.phpt
index 5e53b706a..80d718b3b 100644
--- a/tests/Utils/Object.arrayProperty.phpt
+++ b/tests/Utils/Object.arrayProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object array property.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.closureProperty.phpt b/tests/Utils/Object.closureProperty.phpt
index bbd785f82..82867f3dc 100644
--- a/tests/Utils/Object.closureProperty.phpt
+++ b/tests/Utils/Object.closureProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object closure properties.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.events.phpt b/tests/Utils/Object.events.phpt
index 246b2f17f..da73dcbf9 100644
--- a/tests/Utils/Object.events.phpt
+++ b/tests/Utils/Object.events.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object event handlers.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.extensionMethod.phpt b/tests/Utils/Object.extensionMethod.phpt
index 25fbc3659..aedd97379 100644
--- a/tests/Utils/Object.extensionMethod.phpt
+++ b/tests/Utils/Object.extensionMethod.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object extension method.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.extensionMethodViaInterface.phpt b/tests/Utils/Object.extensionMethodViaInterface.phpt
index d03d3ae2b..b5b226b66 100644
--- a/tests/Utils/Object.extensionMethodViaInterface.phpt
+++ b/tests/Utils/Object.extensionMethodViaInterface.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object extension method via interface.
  */
 
+declare(strict_types=1);
+
 use Nette\Object;
 use Tester\Assert;
 
diff --git a/tests/Utils/Object.magicMethod.errors.phpt b/tests/Utils/Object.magicMethod.errors.phpt
index 404c1f59a..0cfaec340 100644
--- a/tests/Utils/Object.magicMethod.errors.phpt
+++ b/tests/Utils/Object.magicMethod.errors.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object magic @methods errors.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.magicMethod.inheritance.phpt b/tests/Utils/Object.magicMethod.inheritance.phpt
index 5e5d6ccfc..3fea5bf71 100644
--- a/tests/Utils/Object.magicMethod.inheritance.phpt
+++ b/tests/Utils/Object.magicMethod.inheritance.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object magic @methods inheritance.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.magicMethod.phpt b/tests/Utils/Object.magicMethod.phpt
index b9dcdf7e0..7844a2a1a 100644
--- a/tests/Utils/Object.magicMethod.phpt
+++ b/tests/Utils/Object.magicMethod.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object magic @methods.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.magicMethod.types.phpt b/tests/Utils/Object.magicMethod.types.phpt
index dea9a6bb2..c3f265ac1 100644
--- a/tests/Utils/Object.magicMethod.types.phpt
+++ b/tests/Utils/Object.magicMethod.types.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object magic @methods and types.
  */
 
+declare(strict_types=1);
+
 namespace Test;
 
 use Nette;
diff --git a/tests/Utils/Object.methodGetter.phpt b/tests/Utils/Object.methodGetter.phpt
index d090123df..e30f21f85 100644
--- a/tests/Utils/Object.methodGetter.phpt
+++ b/tests/Utils/Object.methodGetter.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object closure properties.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.property.phpt b/tests/Utils/Object.property.phpt
index eed1bb283..0e4a7b86a 100644
--- a/tests/Utils/Object.property.phpt
+++ b/tests/Utils/Object.property.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object properties.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.referenceProperty.phpt b/tests/Utils/Object.referenceProperty.phpt
index e64c5357c..bafe908f2 100644
--- a/tests/Utils/Object.referenceProperty.phpt
+++ b/tests/Utils/Object.referenceProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object reference to property.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.reflection.phpt b/tests/Utils/Object.reflection.phpt
index 38246bcf2..ae8d6ed87 100644
--- a/tests/Utils/Object.reflection.phpt
+++ b/tests/Utils/Object.reflection.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object reflection.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.undeclaredMethod.phpt b/tests/Utils/Object.undeclaredMethod.phpt
index 8470f1453..3c41e08af 100644
--- a/tests/Utils/Object.undeclaredMethod.phpt
+++ b/tests/Utils/Object.undeclaredMethod.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object undeclared method.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Object.unsetProperty.phpt b/tests/Utils/Object.unsetProperty.phpt
index 855e6e87c..a1e6181ed 100644
--- a/tests/Utils/Object.unsetProperty.phpt
+++ b/tests/Utils/Object.unsetProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Object properties.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/ObjectMixin.checkType().phpt b/tests/Utils/ObjectMixin.checkType().phpt
index 9b4ebf2cc..8bf5f97b6 100644
--- a/tests/Utils/ObjectMixin.checkType().phpt
+++ b/tests/Utils/ObjectMixin.checkType().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\ObjectMixin::checkType()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\ObjectMixin;
 use Tester\Assert;
 
diff --git a/tests/Utils/ObjectMixin.getMagicProperites().phpt b/tests/Utils/ObjectMixin.getMagicProperites().phpt
index 05be56bbd..87c6a1d11 100644
--- a/tests/Utils/ObjectMixin.getMagicProperites().phpt
+++ b/tests/Utils/ObjectMixin.getMagicProperites().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\ObjectMixin::getMagicProperties()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\ObjectMixin;
 use Tester\Assert;
 
diff --git a/tests/Utils/ObjectMixin.getSuggestion().phpt b/tests/Utils/ObjectMixin.getSuggestion().phpt
index c1e9987d7..4764ff1e9 100644
--- a/tests/Utils/ObjectMixin.getSuggestion().phpt
+++ b/tests/Utils/ObjectMixin.getSuggestion().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\ObjectMixin::getSuggestion()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\ObjectMixin;
 use Tester\Assert;
 
diff --git a/tests/Utils/ObjectMixin.strictness.phpt b/tests/Utils/ObjectMixin.strictness.phpt
index ed7a9f859..51ae5df03 100644
--- a/tests/Utils/ObjectMixin.strictness.phpt
+++ b/tests/Utils/ObjectMixin.strictness.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\ObjectMixin: strictness
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 use Nette\Utils\ObjectMixin;
 use Nette\MemberAccessException;
diff --git a/tests/Utils/Paginator.phpt b/tests/Utils/Paginator.phpt
index f94fae9c9..b43d20c00 100644
--- a/tests/Utils/Paginator.phpt
+++ b/tests/Utils/Paginator.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Paginator Base:0 Page:3 test.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Paginator;
 use Tester\Assert;
 
diff --git a/tests/Utils/Random.generate().no-mcrypt.phpt b/tests/Utils/Random.generate().no-mcrypt.phpt
index a35938503..03dee73f7 100644
--- a/tests/Utils/Random.generate().no-mcrypt.phpt
+++ b/tests/Utils/Random.generate().no-mcrypt.phpt
@@ -6,6 +6,8 @@
  * @phpversion <7
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Random;
 use Tester\Assert;
 
diff --git a/tests/Utils/Random.generate().no-openssl.phpt b/tests/Utils/Random.generate().no-openssl.phpt
index bca682067..b113a2292 100644
--- a/tests/Utils/Random.generate().no-openssl.phpt
+++ b/tests/Utils/Random.generate().no-openssl.phpt
@@ -6,6 +6,8 @@
  * @phpversion <7
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Random;
 use Tester\Assert;
 
diff --git a/tests/Utils/Random.generate().phpt b/tests/Utils/Random.generate().phpt
index b60bdb4da..c099d94b4 100644
--- a/tests/Utils/Random.generate().phpt
+++ b/tests/Utils/Random.generate().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Random::generate()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Random;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.expandClassName.phpt b/tests/Utils/Reflection.expandClassName.phpt
index 7caf3b9d1..3de371383 100644
--- a/tests/Utils/Reflection.expandClassName.phpt
+++ b/tests/Utils/Reflection.expandClassName.phpt
@@ -4,6 +4,8 @@
  * Test: Expanding class alias to FQN.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.getParameterDefaultValue.phpt b/tests/Utils/Reflection.getParameterDefaultValue.phpt
index 06a3e4845..e75d9aeb8 100644
--- a/tests/Utils/Reflection.getParameterDefaultValue.phpt
+++ b/tests/Utils/Reflection.getParameterDefaultValue.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Reflection::getParameterDefaultValue()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.getParameterType.php71.phpt b/tests/Utils/Reflection.getParameterType.php71.phpt
index 6aacd312f..1254d79da 100644
--- a/tests/Utils/Reflection.getParameterType.php71.phpt
+++ b/tests/Utils/Reflection.getParameterType.php71.phpt
@@ -5,6 +5,8 @@
  * @phpversion 7.1
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.getParameterType.phpt b/tests/Utils/Reflection.getParameterType.phpt
index 93f74d970..dd4952ef0 100644
--- a/tests/Utils/Reflection.getParameterType.phpt
+++ b/tests/Utils/Reflection.getParameterType.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Reflection::getParameterType
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.getPropertyDeclaringClass.phpt b/tests/Utils/Reflection.getPropertyDeclaringClass.phpt
index 97a1459e3..86f390596 100644
--- a/tests/Utils/Reflection.getPropertyDeclaringClass.phpt
+++ b/tests/Utils/Reflection.getPropertyDeclaringClass.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Reflection::getPropertyDeclaringClass
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.getReturnType.php7.phpt b/tests/Utils/Reflection.getReturnType.php7.phpt
index 3846668f2..095fc3fb8 100644
--- a/tests/Utils/Reflection.getReturnType.php7.phpt
+++ b/tests/Utils/Reflection.getReturnType.php7.phpt
@@ -5,6 +5,8 @@
  * @phpversion 7
  */
 
+declare(strict_types=1);
+
 namespace NS
 {
 	use Test\B;
diff --git a/tests/Utils/Reflection.getReturnType.php71.phpt b/tests/Utils/Reflection.getReturnType.php71.phpt
index e401be936..ba90c88cf 100644
--- a/tests/Utils/Reflection.getReturnType.php71.phpt
+++ b/tests/Utils/Reflection.getReturnType.php71.phpt
@@ -5,6 +5,8 @@
  * @phpversion 7.1
  */
 
+declare(strict_types=1);
+
 namespace NS
 {
 	use Test\B;
diff --git a/tests/Utils/Reflection.groupUseStatements.phpt b/tests/Utils/Reflection.groupUseStatements.phpt
index 6b556b1e8..dfa83505e 100644
--- a/tests/Utils/Reflection.groupUseStatements.phpt
+++ b/tests/Utils/Reflection.groupUseStatements.phpt
@@ -5,6 +5,8 @@
  * @phpVersion 7
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.nonClassUseStatements.phpt b/tests/Utils/Reflection.nonClassUseStatements.phpt
index 5932c3433..eb2059c24 100644
--- a/tests/Utils/Reflection.nonClassUseStatements.phpt
+++ b/tests/Utils/Reflection.nonClassUseStatements.phpt
@@ -5,6 +5,8 @@
  * @phpVersion 7
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/Reflection.toString.phpt b/tests/Utils/Reflection.toString.phpt
index 0861df131..678820a53 100644
--- a/tests/Utils/Reflection.toString.phpt
+++ b/tests/Utils/Reflection.toString.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Reflection::toString()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Reflection;
 use Tester\Assert;
 
diff --git a/tests/Utils/SmartObject.arrayProperty.phpt b/tests/Utils/SmartObject.arrayProperty.phpt
index a9f0690b2..407b6fd72 100644
--- a/tests/Utils/SmartObject.arrayProperty.phpt
+++ b/tests/Utils/SmartObject.arrayProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject array property.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.events.phpt b/tests/Utils/SmartObject.events.phpt
index e47e4d15f..caf53d8c5 100644
--- a/tests/Utils/SmartObject.events.phpt
+++ b/tests/Utils/SmartObject.events.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject event handlers.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.property.inheritance.phpt b/tests/Utils/SmartObject.property.inheritance.phpt
index 08a96cb81..80dd51bb5 100644
--- a/tests/Utils/SmartObject.property.inheritance.phpt
+++ b/tests/Utils/SmartObject.property.inheritance.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject properties and inheritance.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.property.phpt b/tests/Utils/SmartObject.property.phpt
index 099966213..379ce92ee 100644
--- a/tests/Utils/SmartObject.property.phpt
+++ b/tests/Utils/SmartObject.property.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject properties.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.referenceProperty.phpt b/tests/Utils/SmartObject.referenceProperty.phpt
index cc987c4a1..ba09035b9 100644
--- a/tests/Utils/SmartObject.referenceProperty.phpt
+++ b/tests/Utils/SmartObject.referenceProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject reference to property.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.undeclaredMethod.annotation.phpt b/tests/Utils/SmartObject.undeclaredMethod.annotation.phpt
index 5c3b5a545..56b898bb6 100644
--- a/tests/Utils/SmartObject.undeclaredMethod.annotation.phpt
+++ b/tests/Utils/SmartObject.undeclaredMethod.annotation.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject undeclared method and annotation @method.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.undeclaredMethod.phpt b/tests/Utils/SmartObject.undeclaredMethod.phpt
index d63961187..e49ebe125 100644
--- a/tests/Utils/SmartObject.undeclaredMethod.phpt
+++ b/tests/Utils/SmartObject.undeclaredMethod.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject undeclared method.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/SmartObject.unsetProperty.phpt b/tests/Utils/SmartObject.unsetProperty.phpt
index 0472f9ff0..2a3b636bd 100644
--- a/tests/Utils/SmartObject.unsetProperty.phpt
+++ b/tests/Utils/SmartObject.unsetProperty.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\SmartObject properties.
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/StaticClass.phpt b/tests/Utils/StaticClass.phpt
index 094d20368..27e4145a4 100644
--- a/tests/Utils/StaticClass.phpt
+++ b/tests/Utils/StaticClass.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\StaticClass
  */
 
+declare(strict_types=1);
+
 use Tester\Assert;
 
 require __DIR__ . '/../bootstrap.php';
diff --git a/tests/Utils/Strings.Regexp.errors.backtrack.phpt b/tests/Utils/Strings.Regexp.errors.backtrack.phpt
index d20e1272e..54091158e 100644
--- a/tests/Utils/Strings.Regexp.errors.backtrack.phpt
+++ b/tests/Utils/Strings.Regexp.errors.backtrack.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings and RegexpException run-time error.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.Regexp.errors.compilation.phpt b/tests/Utils/Strings.Regexp.errors.compilation.phpt
index c59ddd562..09cf0f736 100644
--- a/tests/Utils/Strings.Regexp.errors.compilation.phpt
+++ b/tests/Utils/Strings.Regexp.errors.compilation.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings and RegexpException compile error.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.Regexp.errors.utf8.phpt b/tests/Utils/Strings.Regexp.errors.utf8.phpt
index 795185841..0c6c7f4c6 100644
--- a/tests/Utils/Strings.Regexp.errors.utf8.phpt
+++ b/tests/Utils/Strings.Regexp.errors.utf8.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings and RegexpException run-time error.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.after().phpt b/tests/Utils/Strings.after().phpt
index fbd88b5fc..ef8a92d94 100644
--- a/tests/Utils/Strings.after().phpt
+++ b/tests/Utils/Strings.after().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::after()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.before().phpt b/tests/Utils/Strings.before().phpt
index 3d8deba0e..95e7a243b 100644
--- a/tests/Utils/Strings.before().phpt
+++ b/tests/Utils/Strings.before().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::before()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.checkEncoding().phpt b/tests/Utils/Strings.checkEncoding().phpt
index 3c8f737de..a1d86fcfb 100644
--- a/tests/Utils/Strings.checkEncoding().phpt
+++ b/tests/Utils/Strings.checkEncoding().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::checkEncoding()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.chr().phpt b/tests/Utils/Strings.chr().phpt
index acfa9f828..96e7edd54 100644
--- a/tests/Utils/Strings.chr().phpt
+++ b/tests/Utils/Strings.chr().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::chr()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.compare().phpt b/tests/Utils/Strings.compare().phpt
index 14ea8be27..eb4363c00 100644
--- a/tests/Utils/Strings.compare().phpt
+++ b/tests/Utils/Strings.compare().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::compare()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.convertCase.phpt b/tests/Utils/Strings.convertCase.phpt
index c8f2d86e0..34347b7c5 100644
--- a/tests/Utils/Strings.convertCase.phpt
+++ b/tests/Utils/Strings.convertCase.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings and lower, upper, firstLower, firstUpper, capitalize
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.endsWith().phpt b/tests/Utils/Strings.endsWith().phpt
index a2fc4c2ab..b91d71ad4 100644
--- a/tests/Utils/Strings.endsWith().phpt
+++ b/tests/Utils/Strings.endsWith().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::endsWith()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
@@ -11,7 +13,9 @@ use Tester\Assert;
 require __DIR__ . '/../bootstrap.php';
 
 
-Assert::true(Strings::endsWith('123', NULL), "endsWith('123', NULL)");
+Assert::exception(function () {
+	Strings::endsWith('123', NULL);
+}, TypeError::class);
 Assert::true(Strings::endsWith('123', ''), "endsWith('123', '')");
 Assert::true(Strings::endsWith('123', '3'), "endsWith('123', '3')");
 Assert::false(Strings::endsWith('123', '2'), "endsWith('123', '2')");
diff --git a/tests/Utils/Strings.findPrefix().phpt b/tests/Utils/Strings.findPrefix().phpt
index dbb54fd54..03fa41251 100644
--- a/tests/Utils/Strings.findPrefix().phpt
+++ b/tests/Utils/Strings.findPrefix().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::findPrefix()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.fixEncoding().phpt b/tests/Utils/Strings.fixEncoding().phpt
index cf6396ada..bd212ddb0 100644
--- a/tests/Utils/Strings.fixEncoding().phpt
+++ b/tests/Utils/Strings.fixEncoding().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::fixEncoding()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.indent().phpt b/tests/Utils/Strings.indent().phpt
index 6843d075e..54a79f3c4 100644
--- a/tests/Utils/Strings.indent().phpt
+++ b/tests/Utils/Strings.indent().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::indent()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.indexOf().phpt b/tests/Utils/Strings.indexOf().phpt
index 99383fe68..749afd6bd 100644
--- a/tests/Utils/Strings.indexOf().phpt
+++ b/tests/Utils/Strings.indexOf().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::indexOf()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.length().phpt b/tests/Utils/Strings.length().phpt
index c808213ac..5dc7062fe 100644
--- a/tests/Utils/Strings.length().phpt
+++ b/tests/Utils/Strings.length().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::length()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.match().phpt b/tests/Utils/Strings.match().phpt
index 10c91a613..013922460 100644
--- a/tests/Utils/Strings.match().phpt
+++ b/tests/Utils/Strings.match().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::match()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.matchAll().phpt b/tests/Utils/Strings.matchAll().phpt
index 2806efad1..d228e0e93 100644
--- a/tests/Utils/Strings.matchAll().phpt
+++ b/tests/Utils/Strings.matchAll().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::matchAll()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.normalize().phpt b/tests/Utils/Strings.normalize().phpt
index da298039e..cb72566e2 100644
--- a/tests/Utils/Strings.normalize().phpt
+++ b/tests/Utils/Strings.normalize().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::normalize()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.normalizeNewLines().phpt b/tests/Utils/Strings.normalizeNewLines().phpt
index 67565fbaa..c26223025 100644
--- a/tests/Utils/Strings.normalizeNewLines().phpt
+++ b/tests/Utils/Strings.normalizeNewLines().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::normalizeNewLines()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.pad.phpt b/tests/Utils/Strings.pad.phpt
index eac150ee7..a01cbfd0c 100644
--- a/tests/Utils/Strings.pad.phpt
+++ b/tests/Utils/Strings.pad.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::padLeft() & padRight()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.replace().errors.callback.phpt b/tests/Utils/Strings.replace().errors.callback.phpt
index 0182053e6..9f7c9a473 100644
--- a/tests/Utils/Strings.replace().errors.callback.phpt
+++ b/tests/Utils/Strings.replace().errors.callback.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings and error in callback.
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.replace().php53.phpt b/tests/Utils/Strings.replace().php53.phpt
index 7a87fd4ae..3ddfa402c 100644
--- a/tests/Utils/Strings.replace().php53.phpt
+++ b/tests/Utils/Strings.replace().php53.phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::replace()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.replace().phpt b/tests/Utils/Strings.replace().phpt
index 6a09dcf4e..3d329ea23 100644
--- a/tests/Utils/Strings.replace().phpt
+++ b/tests/Utils/Strings.replace().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::replace()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.reverse().phpt b/tests/Utils/Strings.reverse().phpt
index 1407cad90..66fe5c6b0 100644
--- a/tests/Utils/Strings.reverse().phpt
+++ b/tests/Utils/Strings.reverse().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::reverse()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.split().phpt b/tests/Utils/Strings.split().phpt
index b77d7a4bd..cd516e3aa 100644
--- a/tests/Utils/Strings.split().phpt
+++ b/tests/Utils/Strings.split().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::split()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.startsWith().phpt b/tests/Utils/Strings.startsWith().phpt
index b6f6559bf..c17d22e0e 100644
--- a/tests/Utils/Strings.startsWith().phpt
+++ b/tests/Utils/Strings.startsWith().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::startsWith()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
@@ -11,7 +13,9 @@ use Tester\Assert;
 require __DIR__ . '/../bootstrap.php';
 
 
-Assert::true(Strings::startsWith('123', NULL), "startsWith('123', NULL)");
+Assert::exception(function () {
+	Strings::startsWith('123', NULL);
+}, TypeError::class);
 Assert::true(Strings::startsWith('123', ''), "startsWith('123', '')");
 Assert::true(Strings::startsWith('123', '1'), "startsWith('123', '1')");
 Assert::false(Strings::startsWith('123', '2'), "startsWith('123', '2')");
diff --git a/tests/Utils/Strings.substring().phpt b/tests/Utils/Strings.substring().phpt
index 69ffd4dc5..3a98eb2d5 100644
--- a/tests/Utils/Strings.substring().phpt
+++ b/tests/Utils/Strings.substring().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::substring()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.toAscii().phpt b/tests/Utils/Strings.toAscii().phpt
index 317a80c1e..f2791b76a 100644
--- a/tests/Utils/Strings.toAscii().phpt
+++ b/tests/Utils/Strings.toAscii().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::toAscii()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.trim().phpt b/tests/Utils/Strings.trim().phpt
index c71974733..5736d10ac 100644
--- a/tests/Utils/Strings.trim().phpt
+++ b/tests/Utils/Strings.trim().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::trim()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.truncate().phpt b/tests/Utils/Strings.truncate().phpt
index 2d2ed933a..69ed51475 100644
--- a/tests/Utils/Strings.truncate().phpt
+++ b/tests/Utils/Strings.truncate().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::truncate()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Strings.webalize().phpt b/tests/Utils/Strings.webalize().phpt
index dfc516448..fec21a8da 100644
--- a/tests/Utils/Strings.webalize().phpt
+++ b/tests/Utils/Strings.webalize().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Strings::webalize()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Strings;
 use Tester\Assert;
 
diff --git a/tests/Utils/Validators.assert().phpt b/tests/Utils/Validators.assert().phpt
index bd647b11c..8a8fbdc30 100644
--- a/tests/Utils/Validators.assert().phpt
+++ b/tests/Utils/Validators.assert().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Validators::assert()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Validators;
 use Tester\Assert;
 
diff --git a/tests/Utils/Validators.assertField().phpt b/tests/Utils/Validators.assertField().phpt
index 9e5729fdf..5eeb9a9ba 100644
--- a/tests/Utils/Validators.assertField().phpt
+++ b/tests/Utils/Validators.assertField().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Validators::assertField()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Validators;
 use Tester\Assert;
 
diff --git a/tests/Utils/Validators.everyIs().phpt b/tests/Utils/Validators.everyIs().phpt
index e6a1783d1..453bbcb8e 100644
--- a/tests/Utils/Validators.everyIs().phpt
+++ b/tests/Utils/Validators.everyIs().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Validators::everyIs()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Validators;
 use Tester\Assert;
 
diff --git a/tests/Utils/Validators.is().phpt b/tests/Utils/Validators.is().phpt
index 001eeddab..74a3ab204 100644
--- a/tests/Utils/Validators.is().phpt
+++ b/tests/Utils/Validators.is().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Validators::is()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Validators;
 use Tester\Assert;
 
diff --git a/tests/Utils/Validators.isInRange().phpt b/tests/Utils/Validators.isInRange().phpt
index 77dfc3974..db42f6ed4 100644
--- a/tests/Utils/Validators.isInRange().phpt
+++ b/tests/Utils/Validators.isInRange().phpt
@@ -4,6 +4,8 @@
  * Test: Nette\Utils\Validators::isInRange()
  */
 
+declare(strict_types=1);
+
 use Nette\Utils\Validators;
 use Tester\Assert;
 
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 066985b9a..d543829d6 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -3,6 +3,8 @@
 // The Nette Tester command-line runner can be
 // invoked through the command: ../vendor/bin/tester .
 
+declare(strict_types=1);
+
 if (@!include __DIR__ . '/../vendor/autoload.php') {
 	echo 'Install Nette Tester using `composer install`';
 	exit(1);