diff --git a/tests/unit/Moment/MomentBritishEnglishLocaleTest.php b/tests/unit/Moment/MomentBritishEnglishLocaleTest.php
index 5de9a3e..a2f19f1 100644
--- a/tests/unit/Moment/MomentBritishEnglishLocaleTest.php
+++ b/tests/unit/Moment/MomentBritishEnglishLocaleTest.php
@@ -15,7 +15,7 @@ public function setUp(): void
         Moment::setLocale('en_GB');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -39,7 +39,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -68,7 +68,7 @@ public function testMonthNames()
         }
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $a = array(
             array('l, d F Y, G:i:s', 'Saturday, 12 June 2010, 22:00:00'),
@@ -105,7 +105,7 @@ public function testFormat()
 //        }
 //    }
 
-    public function testOrdinalsFormat()
+    public function testOrdinalsFormat(): void
     {
         $moment = new Moment('2010-06-02T00:00:00+0000');
         self::assertEquals('2nd', $moment->format('jS'));
@@ -113,7 +113,7 @@ public function testOrdinalsFormat()
         self::assertEquals('12th', $moment->format('jS'));
     }
 
-	public function testRelative()
+	public function testRelative(): void
 	{
 		Moment::setLocale('en_GB');
 
diff --git a/tests/unit/Moment/MomentCanadianEnglishLocaleTest.php b/tests/unit/Moment/MomentCanadianEnglishLocaleTest.php
index 16475b2..e28074d 100644
--- a/tests/unit/Moment/MomentCanadianEnglishLocaleTest.php
+++ b/tests/unit/Moment/MomentCanadianEnglishLocaleTest.php
@@ -24,7 +24,7 @@ public function setUp(): void
         Moment::setLocale('en_CA');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -48,7 +48,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -77,7 +77,7 @@ public function testMonthNames()
         }
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $a = array(
             array('l, d F Y, G:i:s', 'Saturday, 12 June 2010, 22:00:00'),
@@ -93,7 +93,7 @@ public function testFormat()
         }
     }
 
-    public function testCustomLocaleFormat()
+    public function testCustomLocaleFormat(): void
     {
         $a = array(
             array('LT', '10:00 PM',),
@@ -114,7 +114,7 @@ public function testCustomLocaleFormat()
         }
     }
 
-    public function testOrdinalsFormat()
+    public function testOrdinalsFormat(): void
     {
         $moment = new Moment('2010-06-02T00:00:00+0000');
         self::assertEquals('2nd', $moment->format('jS'));
@@ -122,7 +122,7 @@ public function testOrdinalsFormat()
         self::assertEquals('12th', $moment->format('jS'));
     }
 
-	public function testRelative()
+	public function testRelative(): void
 	{
 		$beginningMoment = new Moment('2010-06-12 00:00:00', 'Europe/London');
 
diff --git a/tests/unit/Moment/MomentCanadianFrenchLocaleTest.php b/tests/unit/Moment/MomentCanadianFrenchLocaleTest.php
index dd089a8..f2ccd57 100755
--- a/tests/unit/Moment/MomentCanadianFrenchLocaleTest.php
+++ b/tests/unit/Moment/MomentCanadianFrenchLocaleTest.php
@@ -23,7 +23,7 @@ public function setUp(): void
         Moment::setLocale('fr_CA');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -48,7 +48,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -78,7 +78,7 @@ public function testMonthNames()
         }
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $a = array(
             array('l, F d Y, g:i:s a', 'dimanche, février 14 2010, 3:25:50 pm'),
@@ -94,7 +94,7 @@ public function testFormat()
         }
     }
 
-    public function testOrdinalsFormat()
+    public function testOrdinalsFormat(): void
     {
         $moment = new Moment('2010-06-02T00:00:00+0000');
         self::assertEquals('2', $moment->format('jS'));
@@ -102,7 +102,7 @@ public function testOrdinalsFormat()
         self::assertEquals('1er', $moment->format('jS'));
     }
 
-    public function testRelative()
+    public function testRelative(): void
     {
         $beginningMoment = new Moment('2015-06-14 20:46:22', 'Europe/Berlin');
         $endMoment = new Moment('2015-06-14 20:48:32', 'Europe/Berlin');
diff --git a/tests/unit/Moment/MomentEsperantoLocaleTest.php b/tests/unit/Moment/MomentEsperantoLocaleTest.php
index c4c67b5..bdf2fac 100644
--- a/tests/unit/Moment/MomentEsperantoLocaleTest.php
+++ b/tests/unit/Moment/MomentEsperantoLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('eo');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -35,7 +35,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -64,7 +64,7 @@ public function testMonthNames()
         }
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $targetDate = new Moment('2010-06-09 15:25:50');
         $formats = array(
@@ -82,7 +82,7 @@ public function testFormat()
         }
     }
 
-    public function _testRelative()
+    public function _testRelative(): void
     {
         $beginningMoment = new Moment('2015-06-14 20:46:22', 'Europe/Berlin');
         $endMoment = new Moment('2015-06-14 20:48:32', 'Europe/Berlin');
@@ -90,7 +90,7 @@ public function _testRelative()
         self::assertEquals('antaŭ 2 minutoj', $beginningMoment->from($endMoment)->getRelative());
     }
 
-    public function testRelative()
+    public function testRelative(): void
     {
         $tz = 'Europe/Berlin';
         $beginningMoment = new Moment('2010-06-12 00:00:00', $tz);
diff --git a/tests/unit/Moment/MomentFrenchLocaleTest.php b/tests/unit/Moment/MomentFrenchLocaleTest.php
index 8ac83fd..2a7632f 100755
--- a/tests/unit/Moment/MomentFrenchLocaleTest.php
+++ b/tests/unit/Moment/MomentFrenchLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('fr_FR');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -36,7 +36,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -66,7 +66,7 @@ public function testMonthNames()
         }
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $a = array(
             array('l, F d Y, g:i:s a',                  'dimanche, février 14 2010, 3:25:50 pm'),
@@ -82,7 +82,7 @@ public function testFormat()
         }
     }
 
-    public function testRelative()
+    public function testRelative(): void
     {
         $beginningMoment = new Moment('2015-06-14 20:46:22', 'Europe/Berlin');
         $endMoment = new Moment('2015-06-14 20:48:32', 'Europe/Berlin');
diff --git a/tests/unit/Moment/MomentGermanLocaleTest.php b/tests/unit/Moment/MomentGermanLocaleTest.php
index 8fa6066..dc47734 100755
--- a/tests/unit/Moment/MomentGermanLocaleTest.php
+++ b/tests/unit/Moment/MomentGermanLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('de_DE');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -36,7 +36,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -66,7 +66,7 @@ public function testMonthNames()
         }
     }
 
-    public function testHirbodIssueLocaleDate001()
+    public function testHirbodIssueLocaleDate001(): void
     {
         // @see: https://github.com/fightbulc/moment.php/issues/50
 
@@ -79,7 +79,7 @@ public function testHirbodIssueLocaleDate001()
         self::assertEquals('08. März', $moment->format('d. F'));
     }
 
-    public function testHirbodIssueLocaleDate002()
+    public function testHirbodIssueLocaleDate002(): void
     {
         // @see: https://github.com/fightbulc/moment.php/issues/61
 
@@ -87,7 +87,7 @@ public function testHirbodIssueLocaleDate002()
         self::assertEquals('03. Dezember', $moment->subtractMonths(1)->format('d. F'));
     }
 
-    public function testMonthsNominativeFallback()
+    public function testMonthsNominativeFallback(): void
     {
         $moment = new Moment('2016-01-03 16:17:07', 'Europe/Berlin');
         self::assertEquals('Januar 2016', $moment->format('f Y'));
diff --git a/tests/unit/Moment/MomentLatvianLocaleTest.php b/tests/unit/Moment/MomentLatvianLocaleTest.php
index 389d994..06819dd 100755
--- a/tests/unit/Moment/MomentLatvianLocaleTest.php
+++ b/tests/unit/Moment/MomentLatvianLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('lv_LV');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2017-10-20T00:00:00+0000';
 
@@ -46,7 +46,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthFormat()
+    public function testMonthFormat(): void
     {
         $startingDate = '2016-01-01T00:00:00+0000';
 
@@ -94,7 +94,7 @@ public function testMonthFormat()
         }
     }
 
-    public function testDayMonthFormat001()
+    public function testDayMonthFormat001(): void
     {
         $string = '2015-06-14 20:46:22';
         $moment = new Moment($string, 'Europe/Riga');
@@ -105,7 +105,7 @@ public function testDayMonthFormat001()
         self::assertEquals('8 Martā', $moment->format('j F'));
     }
 
-    public function testMinutes()
+    public function testMinutes(): void
     {
         $past = new Moment('2016-01-03 16:17:07', 'Europe/Riga');
 
@@ -113,7 +113,7 @@ public function testMinutes()
         self::assertEquals('pirms 17 minūtēm', $relative->getRelative());
     }
 
-    public function testShowRelativeCalendarDates()
+    public function testShowRelativeCalendarDates(): void
     {
         $past = new Moment('2016-04-10 16:30:07');
         self::assertEquals('Pagājušā Svētdiena plkst. 16:30', $past->calendar(true, new Moment('2016-04-12')));
@@ -137,7 +137,7 @@ public function testShowRelativeCalendarDates()
         self::assertEquals('15.04.2116', $past->calendar(false, new Moment('2017-04-23')));
     }
 
-    public function testFutureRelative()
+    public function testFutureRelative(): void
     {
         $date = new Moment('2017-01-11 01:00:00');
 
@@ -153,7 +153,7 @@ public function testFutureRelative()
         self::assertEquals('pēc 7 gadiem', $date->from('2010-01-11 00:00:00')->getRelative(), 'year');
     }
 
-    public function testPastRelative()
+    public function testPastRelative(): void
     {
         $date = new Moment('2010-01-11 01:00:00');
         self::assertEquals('pirms dažām sekundēm', $date->from('2010-01-11 01:00:01')->getRelative(), 'seconds');
@@ -168,7 +168,7 @@ public function testPastRelative()
         self::assertEquals('pirms 5 gadiem', $date->from('2015-01-11 01:00:00')->getRelative(), 'year');
     }
 
-    public function testOrdinalFormat()
+    public function testOrdinalFormat(): void
     {
         $date = new Moment('2017-01-01 01:00:00', 'Europe/Riga');
         self::assertEquals('1. Janvāris 2017', $date->format('jS f Y'));
diff --git a/tests/unit/Moment/MomentPolishLocaleTest.php b/tests/unit/Moment/MomentPolishLocaleTest.php
index fddd9a9..88f7133 100755
--- a/tests/unit/Moment/MomentPolishLocaleTest.php
+++ b/tests/unit/Moment/MomentPolishLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('pl_PL');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2016-01-29T00:00:00+0000';
 
@@ -35,7 +35,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testDayMonthFormat001()
+    public function testDayMonthFormat001(): void
     {
         $string = '2015-06-14 20:46:22';
         $moment = new Moment($string, 'Europe/Berlin');
@@ -46,13 +46,13 @@ public function testDayMonthFormat001()
         self::assertEquals('8 marca', $moment->format('j F'));
     }
 
-    public function testDayMonthFormat002()
+    public function testDayMonthFormat002(): void
     {
         $moment = new Moment('2016-01-03 16:17:07', 'Europe/Berlin');
         self::assertEquals('3 grudnia', $moment->subtractMonths(1)->format('j F'));
     }
 
-    public function testMonthFormatFN()
+    public function testMonthFormatFN(): void
     {
         $startingDate = '2016-01-01T00:00:00+0000';
 
@@ -81,7 +81,7 @@ public function testMonthFormatFN()
     }
 
 
-    public function testMinutes()
+    public function testMinutes(): void
     {
         $past = new Moment('2016-01-03 16:17:07', 'Europe/Berlin');
 
@@ -95,7 +95,7 @@ public function testMinutes()
         self::assertEquals('13 minut temu', $relative->getRelative());
     }
 
-    public function testLastWeekWeekend()
+    public function testLastWeekWeekend(): void
     {
         $past = new Moment('2016-04-10');
         self::assertEquals('ostatnia niedziela', $past->calendar(false, new Moment('2016-04-12')));
diff --git a/tests/unit/Moment/MomentRussianLocaleTest.php b/tests/unit/Moment/MomentRussianLocaleTest.php
index 480a225..dd6e5d2 100755
--- a/tests/unit/Moment/MomentRussianLocaleTest.php
+++ b/tests/unit/Moment/MomentRussianLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('ru_RU');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2016-01-29T00:00:00+0000';
 
@@ -35,7 +35,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testDayMonthFormat001()
+    public function testDayMonthFormat001(): void
     {
         $string = '2015-06-14 20:46:22';
         $moment = new Moment($string, 'Europe/Moscow');
@@ -46,13 +46,13 @@ public function testDayMonthFormat001()
         self::assertEquals('8 марта', $moment->format('j F'));
     }
 
-    public function testDayMonthFormat002()
+    public function testDayMonthFormat002(): void
     {
         $moment = new Moment('2016-01-03 16:17:07', 'Europe/Moscow');
         self::assertEquals('3 декабря', $moment->subtractMonths(1)->format('j F'));
     }
 
-    public function testMonthFormatFN()
+    public function testMonthFormatFN(): void
     {
         $startingDate = '2016-01-01T00:00:00+0000';
 
@@ -81,7 +81,7 @@ public function testMonthFormatFN()
     }
 
 
-    public function testMinutes()
+    public function testMinutes(): void
     {
         $past = new Moment('2016-01-03 16:17:07', 'Europe/Moscow');
 
@@ -95,7 +95,7 @@ public function testMinutes()
         self::assertEquals('13 минут назад', $relative->getRelative());
     }
 
-    public function testSeconds()
+    public function testSeconds(): void
     {
        $past = new Moment('2017-08-30 20:49:30', 'Europe/Samara');
 
@@ -109,7 +109,7 @@ public function testSeconds()
        self::assertEquals('5 секунд назад', $relative->getRelative());
        }
 
-    public function testLastWeekWeekend()
+    public function testLastWeekWeekend(): void
     {
         $past = new Moment('2016-04-10 16:30:07');
         self::assertEquals('воскресенье в 16:30', $past->calendar(true, new Moment('2016-04-12')));
@@ -136,7 +136,7 @@ public function testLastWeekWeekend()
         self::assertEquals('суббота', $past->calendar(false, new Moment('2016-04-18')));
     }
 
-    public function testFutureRelative()
+    public function testFutureRelative(): void
     {
         $date = new Moment('2017-01-11 01:00:00');
 
@@ -150,7 +150,7 @@ public function testFutureRelative()
     }
 
 
-    public function testOrdinalFormat()
+    public function testOrdinalFormat(): void
     {
         $date = new Moment('2017-01-01 01:00:00');
         self::assertEquals('1е января 2017', $date->format('jS F Y'));
diff --git a/tests/unit/Moment/MomentTurkishLocaleTest.php b/tests/unit/Moment/MomentTurkishLocaleTest.php
index 864a4d1..f73640e 100755
--- a/tests/unit/Moment/MomentTurkishLocaleTest.php
+++ b/tests/unit/Moment/MomentTurkishLocaleTest.php
@@ -16,7 +16,7 @@ public function setUp(): void
         Moment::setLocale('tr_TR');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -39,7 +39,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testMonthNames()
+    public function testMonthNames(): void
     {
         $startingDate = '2015-01-04T00:00:00+0000';
 
@@ -68,7 +68,7 @@ public function testMonthNames()
         }
     }
 
-    public function testFormat()
+    public function testFormat(): void
     {
         $a = array(
             array('l, F d Y, g:i:s a',                  'Pazar, Şubat 14 2010, 3:25:50 pm'),
@@ -84,7 +84,7 @@ public function testFormat()
         }
     }
 
-    public function testRelative()
+    public function testRelative(): void
     {
         $beginningMoment = new Moment('2015-06-14 20:46:22', 'Europe/Istanbul');
         $endMoment = new Moment('2015-06-14 20:48:32', 'Europe/Istanbul');
@@ -92,7 +92,7 @@ public function testRelative()
         self::assertEquals('2 dakika önce', $beginningMoment->from($endMoment)->getRelative());
     }
 
-    public function testMinutes()
+    public function testMinutes(): void
     {
         $past = new Moment('2016-01-03 16:17:07', 'Europe/Kiev');
 
@@ -106,7 +106,7 @@ public function testMinutes()
         self::assertEquals('13 dakika önce', $relative->getRelative());
     }
 
-    public function testLastWeekWeekend()
+    public function testLastWeekWeekend(): void
     {
         $past = new Moment('2016-04-10 16:30:07');
         self::assertEquals('Geçen hafta Pazar 16:30', $past->calendar(true, new Moment('2016-04-12')));
diff --git a/tests/unit/Moment/MomentUkrainianLocaleTest.php b/tests/unit/Moment/MomentUkrainianLocaleTest.php
index 15c26f2..34b7b41 100755
--- a/tests/unit/Moment/MomentUkrainianLocaleTest.php
+++ b/tests/unit/Moment/MomentUkrainianLocaleTest.php
@@ -11,7 +11,7 @@ public function setUp(): void
         Moment::setLocale('uk_UA');
     }
 
-    public function testWeekdayNames()
+    public function testWeekdayNames(): void
     {
         $startingDate = '2016-01-29T00:00:00+0000';
 
@@ -35,7 +35,7 @@ public function testWeekdayNames()
         }
     }
 
-    public function testDayMonthFormat001()
+    public function testDayMonthFormat001(): void
     {
         $string = '2015-06-14 20:46:22';
         $moment = new Moment($string, 'Europe/Kiev');
@@ -46,13 +46,13 @@ public function testDayMonthFormat001()
         self::assertEquals('8 березня', $moment->format('j F'));
     }
 
-    public function testDayMonthFormat002()
+    public function testDayMonthFormat002(): void
     {
         $moment = new Moment('2016-01-03 16:17:07', 'Europe/Kiev');
         self::assertEquals('3 грудня', $moment->subtractMonths(1)->format('j F'));
     }
 
-    public function testMonthFormatFN()
+    public function testMonthFormatFN(): void
     {
         $startingDate = '2016-01-01T00:00:00+0000';
 
@@ -81,7 +81,7 @@ public function testMonthFormatFN()
     }
 
 
-    public function testMinutes()
+    public function testMinutes(): void
     {
         $past = new Moment('2016-01-03 16:17:07', 'Europe/Kiev');
 
@@ -95,7 +95,7 @@ public function testMinutes()
         self::assertEquals('13 хвилин тому', $relative->getRelative());
     }
 
-    public function testLastWeekWeekend()
+    public function testLastWeekWeekend(): void
     {
         $past = new Moment('2016-04-10 16:30:07');
         self::assertEquals('неділя о 16:30', $past->calendar(true, new Moment('2016-04-12')));