Fix Date::roundMicroseconds() not resetting microsecond part

Author: marc-mabe

src/PhpSpreadsheet/Shared/Date.php

@@ -537,11 +537,16 @@ public static function formattedDateTimeFromTimestamp(string $date, string $form
         return $dtobj->format($format);
     }
 
+    /**
+     * Round the given DateTime object to seconds
+     */
     public static function roundMicroseconds(DateTime $dti): void
     {
         $microseconds = (int) $dti->format('u');
-        if ($microseconds >= 500000) {
-            $dti->modify('+1 second');
+        $rounded = (int) round($microseconds, -6);
+        $modify = $rounded - $microseconds;
+        if ($modify !== 0) {
+            $dti->modify(($modify > 0 ? '+' : '') . $modify . ' microseconds');
         }
     }
 }

tests/PhpSpreadsheetTests/Shared/DateTest.php

@@ -249,4 +249,19 @@ public function testVarious(): void
             ->setFormatCode('yyyy-mm-dd');
         self::assertFalse(Date::isDateTime($cella4));
     }
+
+    public function testRoundMicroseconds(): void
+    {
+        $dti = new \DateTime('2000-01-02 03:04:05.999999');
+        Date::roundMicroseconds($dti);
+        static::assertEquals(new \DateTime('2000-01-02 03:04:06.000000'), $dti);
+
+        $dti = new \DateTime('2000-01-02 03:04:05.500000');
+        Date::roundMicroseconds($dti);
+        static::assertEquals(new \DateTime('2000-01-02 03:04:06.000000'), $dti);
+
+        $dti = new \DateTime('2000-01-02 03:04:05.499999');
+        Date::roundMicroseconds($dti);
+        static::assertEquals(new \DateTime('2000-01-02 03:04:05.000000'), $dti);
+    }
 }