diff --git a/lib/Filter.php b/lib/Filter.php
index 60f6f17..d0f1c33 100644
--- a/lib/Filter.php
+++ b/lib/Filter.php
@@ -39,7 +39,9 @@ class Filter
     /**
      * format a given time string into a human readable label (localized)
      *
-     * accepts times in the format "[integer][time unit]"
+     * accepts times in the format "[integer][time unit]", valid time units are:
+     * sec, second, seconds, min, minute, minutes, hour, hours, day, days, week,
+     * weeks, month, months, year, years
      *
      * @access public
      * @static
diff --git a/tst/FilterTest.php b/tst/FilterTest.php
index 63cc8f8..1b40998 100644
--- a/tst/FilterTest.php
+++ b/tst/FilterTest.php
@@ -1,9 +1,12 @@
 <?php
 
 use PrivateBin\Filter;
+use Eris\Generator;
 
 class FilterTest extends PHPUnit_Framework_TestCase
 {
+    use Eris\TestTrait;
+
     public function testFilterStripsSlashesDeeply()
     {
         $this->assertEquals(
@@ -14,10 +17,43 @@ class FilterTest extends PHPUnit_Framework_TestCase
 
     public function testFilterMakesTimesHumanlyReadable()
     {
-        $this->assertEquals('5 minutes', Filter::formatHumanReadableTime('5min'));
-        $this->assertEquals('90 seconds', Filter::formatHumanReadableTime('90sec'));
-        $this->assertEquals('1 week', Filter::formatHumanReadableTime('1week'));
-        $this->assertEquals('6 months', Filter::formatHumanReadableTime('6months'));
+        $this->forAll(
+            Generator\nat(),
+            Generator\oneOf(
+                'sec', 'second', 'seconds'
+            )
+        )->then(
+            function ($int, $unit)
+            {
+                $suffix = $int === 1 ? '' : 's';
+                $this->assertEquals($int . ' second' . $suffix, Filter::formatHumanReadableTime($int . $unit));
+            }
+        );
+        $this->forAll(
+            Generator\nat(),
+            Generator\oneOf(
+                'min', 'minute', 'minutes'
+            )
+        )->then(
+            function ($int, $unit)
+            {
+                $suffix = $int === 1 ? '' : 's';
+                $this->assertEquals($int . ' minute' . $suffix, Filter::formatHumanReadableTime($int . $unit));
+            }
+        );
+        $this->forAll(
+            Generator\nat(),
+            Generator\oneOf(
+                'hour', 'hours', 'day', 'days', 'week', 'weeks',
+                'month', 'months', 'year', 'years'
+            )
+        )->then(
+            function ($int, $unit)
+            {
+                $suffix = $int === 1 ? '' : 's';
+                $this->assertEquals($int . ' ' . rtrim($unit, 's') . $suffix, Filter::formatHumanReadableTime($int . $unit));
+            }
+        );
     }
 
     /**
diff --git a/tst/Vizhash16x16Test.php b/tst/Vizhash16x16Test.php
index 6a6c8a7..a8db074 100644
--- a/tst/Vizhash16x16Test.php
+++ b/tst/Vizhash16x16Test.php
@@ -41,16 +41,14 @@ class Vizhash16x16Test extends PHPUnit_Framework_TestCase
                 $vz      = new Vizhash16x16();
                 $pngdata = $vz->generate($string1);
 
-                if (empty($string1))
-                {
+                if (empty($string1)) {
                     $this->assertEquals($pngdata, '');
                 } else {
                     $this->assertNotEquals($pngdata, '');
                     file_put_contents($this->_file, $pngdata);
                     $finfo = new finfo(FILEINFO_MIME_TYPE);
                     $this->assertEquals('image/png', $finfo->file($this->_file));
-                    if ($string1 !== $string2)
-                    {
+                    if ($string1 !== $string2) {
                         $this->assertNotEquals($pngdata, $string2);
                     }
                 }
@@ -73,8 +71,7 @@ class Vizhash16x16Test extends PHPUnit_Framework_TestCase
                 file_put_contents($this->_file, $pngdata);
                 $finfo = new finfo(FILEINFO_MIME_TYPE);
                 $this->assertEquals('image/png', $finfo->file($this->_file));
-                if ($hash1 !== $hash2)
-                {
+                if ($hash1 !== $hash2) {
                     $this->assertNotEquals($pngdata, $vz->generate($hash2));
                 }
                 $this->assertEquals($pngdata, $vz->generate($hash1));
@@ -96,8 +93,7 @@ class Vizhash16x16Test extends PHPUnit_Framework_TestCase
                 file_put_contents($this->_file, $pngdata);
                 $finfo = new finfo(FILEINFO_MIME_TYPE);
                 $this->assertEquals('image/png', $finfo->file($this->_file));
-                if ($hash1 !== $hash2)
-                {
+                if ($hash1 !== $hash2) {
                     $this->assertNotEquals($pngdata, $vz->generate($hash2));
                 }
                 $this->assertEquals($pngdata, $vz->generate($hash1));