diff --git a/tests/PhpSpreadsheetTests/Shared/DateTest.php b/tests/PhpSpreadsheetTests/Shared/DateTest.php
index c276cf34b..c770ac260 100644
--- a/tests/PhpSpreadsheetTests/Shared/DateTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/DateTest.php
@@ -9,6 +9,7 @@ use DateTimeInterface;
 use DateTimeZone;
 use PhpOffice\PhpSpreadsheet\Exception;
 use PhpOffice\PhpSpreadsheet\Shared\Date;
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
 use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
 use PHPUnit\Framework\TestCase;
 
@@ -207,7 +208,7 @@ class DateTest extends TestCase
         $date = Date::PHPToExcel('2020-01-01');
         self::assertEquals(43831.0, $date);
 
-        $spreadsheet = new \PhpOffice\PhpSpreadsheet\Spreadsheet();
+        $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
         $sheet->setCellValue('B1', 'x');
         /** @var float|int|string */
@@ -249,6 +250,7 @@ class DateTest extends TestCase
             ->getNumberFormat()
             ->setFormatCode('yyyy-mm-dd');
         self::assertFalse(Date::isDateTime($cella4));
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testRoundMicroseconds(): void
diff --git a/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php b/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php
index eb46beaf3..13a58dfe1 100644
--- a/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php
+++ b/tests/PhpSpreadsheetTests/Shared/StringHelperInvalidCharTest.php
@@ -43,5 +43,6 @@ class StringHelperInvalidCharTest extends TestCase
                 $sheet->getCell("A$row")->getValue()
             );
         }
+        $spreadsheet->disconnectWorksheets();
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php b/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php
index 844fa3fb5..8c50ddc17 100644
--- a/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php
+++ b/tests/PhpSpreadsheetTests/Style/BorderRangeTest.php
@@ -62,6 +62,7 @@ class BorderRangeTest extends TestCase
                 }
             }
         }
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testBorderRangeDirectly(): void
@@ -71,5 +72,6 @@ class BorderRangeTest extends TestCase
         $sheet = $spreadsheet->getActiveSheet();
         $style = $sheet->getStyle('A1:C1')->getBorders()->getTop()->setBorderStyle(Border::BORDER_THIN);
         self::assertSame('A1:C1', $style->getSelectedCells(), 'getSelectedCells should not change after a style operation on a border range');
+        $spreadsheet->disconnectWorksheets();
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Style/BorderTest.php b/tests/PhpSpreadsheetTests/Style/BorderTest.php
index 9f18f0766..dfe703213 100644
--- a/tests/PhpSpreadsheetTests/Style/BorderTest.php
+++ b/tests/PhpSpreadsheetTests/Style/BorderTest.php
@@ -31,6 +31,7 @@ class BorderTest extends TestCase
         self::assertSame(Border::BORDER_THIN, $borders->getRight()->getBorderStyle());
         self::assertSame(Border::BORDER_THIN, $borders->getLeft()->getBorderStyle());
         self::assertSame(Border::BORDER_NONE, $borders->getDiagonal()->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testAllBordersArray(): void
@@ -45,6 +46,7 @@ class BorderTest extends TestCase
         self::assertSame(Border::BORDER_THIN, $borders->getRight()->getBorderStyle());
         self::assertSame(Border::BORDER_THIN, $borders->getLeft()->getBorderStyle());
         self::assertSame(Border::BORDER_NONE, $borders->getDiagonal()->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testAllBordersArrayNotSupervisor(): void
@@ -86,6 +88,7 @@ class BorderTest extends TestCase
         self::assertSame(Border::BORDER_THIN, $sheet->getCell('B2')->getStyle()->getBorders()->getBottom()->getBorderStyle());
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getLeft()->getBorderStyle());
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getTop()->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testInside(): void
@@ -115,6 +118,7 @@ class BorderTest extends TestCase
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getBottom()->getBorderStyle());
         self::assertSame(Border::BORDER_THIN, $sheet->getCell('B2')->getStyle()->getBorders()->getLeft()->getBorderStyle());
         self::assertSame(Border::BORDER_THIN, $sheet->getCell('B2')->getStyle()->getBorders()->getTop()->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testHorizontal(): void
@@ -144,6 +148,7 @@ class BorderTest extends TestCase
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getBottom()->getBorderStyle());
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getLeft()->getBorderStyle());
         self::assertSame(Border::BORDER_THIN, $sheet->getCell('B2')->getStyle()->getBorders()->getTop()->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testVertical(): void
@@ -173,6 +178,7 @@ class BorderTest extends TestCase
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getBottom()->getBorderStyle());
         self::assertSame(Border::BORDER_THIN, $sheet->getCell('B2')->getStyle()->getBorders()->getLeft()->getBorderStyle());
         self::assertSame(Border::BORDER_NONE, $sheet->getCell('B2')->getStyle()->getBorders()->getTop()->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testNoSupervisorAllBorders(): void
@@ -213,6 +219,7 @@ class BorderTest extends TestCase
     public function testGetSharedComponentPseudo(): void
     {
         $this->expectException(PhpSpreadsheetException::class);
+        $this->expectExceptionMessage('pseudo-border');
         $spreadsheet = new Spreadsheet();
         $sheet = $spreadsheet->getActiveSheet();
         $sheet->getStyle('A1')->getBorders()->getHorizontal()->setBorderStyle(Border::BORDER_MEDIUM);
@@ -233,6 +240,7 @@ class BorderTest extends TestCase
         $border->setBorderStyle(Border::BORDER_THIN)->setColor(new Color('FFFF0000'));
         self::assertEquals('FFFF0000', $border->getColor()->getARGB());
         self::assertEquals(Border::BORDER_THIN, $border->getBorderStyle());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testDiagonalDirection(): void
@@ -245,5 +253,6 @@ class BorderTest extends TestCase
 
         self::assertSame(Border::BORDER_MEDIUM, $borders->getDiagonal()->getBorderStyle());
         self::assertSame(Borders::DIAGONAL_BOTH, $borders->getDiagonalDirection());
+        $spreadsheet->disconnectWorksheets();
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php
index 04681b39a..5002bcaa1 100644
--- a/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php
+++ b/tests/PhpSpreadsheetTests/Style/ConditionalFormatting/Wizard/WizardFactoryTest.php
@@ -66,6 +66,7 @@ class WizardFactoryTest extends TestCase
             $wizard = Wizard::fromConditional($conditional);
             self::assertEquals($expectedWizads[$index], $wizard::class);
         }
+        $spreadsheet->disconnectWorksheets();
     }
 
     public static function conditionalProvider(): array
diff --git a/tests/PhpSpreadsheetTests/Style/StyleTest.php b/tests/PhpSpreadsheetTests/Style/StyleTest.php
index be67a5e79..6446bcf99 100644
--- a/tests/PhpSpreadsheetTests/Style/StyleTest.php
+++ b/tests/PhpSpreadsheetTests/Style/StyleTest.php
@@ -24,6 +24,7 @@ class StyleTest extends TestCase
         $styleArray = ['alignment' => ['textRotation' => 45]];
         $outArray = $cell1style->getStyleArray($styleArray);
         self::assertEquals($styleArray, $outArray['quotePrefix']);
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testStyleColumn(): void
@@ -58,6 +59,7 @@ class StyleTest extends TestCase
         self::assertTrue($sheet->getStyle('A1')->getFont()->getItalic());
         self::assertTrue($sheet->getStyle('B2')->getFont()->getItalic());
         self::assertFalse($sheet->getStyle('C3')->getFont()->getItalic());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testStyleIsReused(): void
@@ -81,6 +83,7 @@ class StyleTest extends TestCase
         $spreadsheet->garbageCollect();
 
         self::assertCount(3, $spreadsheet->getCellXfCollection());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testStyleRow(): void
@@ -115,6 +118,7 @@ class StyleTest extends TestCase
         self::assertFalse($sheet->getStyle('A1')->getFont()->getItalic());
         self::assertTrue($sheet->getStyle('B2')->getFont()->getItalic());
         self::assertTrue($sheet->getStyle('C3')->getFont()->getItalic());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testIssue1712A(): void
@@ -137,6 +141,7 @@ class StyleTest extends TestCase
             ->setRGB($rgb);
         self::assertEquals($rgb, $sheet->getCell('A1')->getStyle()->getFill()->getStartColor()->getRGB());
         self::assertEquals($rgb, $sheet->getCell('B1')->getStyle()->getFill()->getStartColor()->getRGB());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testIssue1712B(): void
@@ -159,6 +164,7 @@ class StyleTest extends TestCase
         $sheet->fromArray(['OK', 'KO']);
         self::assertEquals($rgb, $sheet->getCell('A1')->getStyle()->getFill()->getStartColor()->getRGB());
         self::assertEquals($rgb, $sheet->getCell('B1')->getStyle()->getFill()->getStartColor()->getRGB());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testStyleLoopUpwards(): void
@@ -184,6 +190,7 @@ class StyleTest extends TestCase
         self::assertFalse($sheet->getStyle('A1')->getFont()->getBold());
         self::assertFalse($sheet->getStyle('B2')->getFont()->getBold());
         self::assertTrue($sheet->getStyle('C3')->getFont()->getBold());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testStyleCellAddressObject(): void
@@ -195,6 +202,7 @@ class StyleTest extends TestCase
         $style->getNumberFormat()->setFormatCode(NumberFormat::FORMAT_DATE_YYYYMMDDSLASH);
 
         self::assertSame(NumberFormat::FORMAT_DATE_YYYYMMDDSLASH, $style->getNumberFormat()->getFormatCode());
+        $spreadsheet->disconnectWorksheets();
     }
 
     public function testStyleCellRangeObject(): void
@@ -208,5 +216,6 @@ class StyleTest extends TestCase
         $style->getNumberFormat()->setFormatCode(NumberFormat::FORMAT_DATE_YYYYMMDDSLASH);
 
         self::assertSame(NumberFormat::FORMAT_DATE_YYYYMMDDSLASH, $style->getNumberFormat()->getFormatCode());
+        $spreadsheet->disconnectWorksheets();
     }
 }
diff --git a/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php b/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php
index 4a4f488bb..558590bfb 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/AutoSizeTest.php
@@ -13,16 +13,14 @@ use PHPUnit\Framework\TestCase;
 
 class AutoSizeTest extends TestCase
 {
-    protected Spreadsheet $spreadsheet;
+    private Spreadsheet $spreadsheet;
 
-    protected Worksheet $worksheet;
+    private Worksheet $worksheet;
 
     protected function setUp(): void
     {
-        parent::setUp();
-
-        $spreadsheet = new Spreadsheet();
-        $this->worksheet = $spreadsheet->getActiveSheet();
+        $this->spreadsheet = new Spreadsheet();
+        $this->worksheet = $this->spreadsheet->getActiveSheet();
 
         $this->worksheet->setCellValue('A1', 'YEAR')
             ->setCellValue('B1', 'QUARTER')
@@ -44,7 +42,13 @@ class AutoSizeTest extends TestCase
         }
     }
 
-    protected function setTable(): Table
+    protected function tearDown(): void
+    {
+        $this->spreadsheet->disconnectWorksheets();
+        unset($this->spreadsheet, $this->worksheet);
+    }
+
+    private function setTable(): Table
     {
         $table = new Table('A1:D5', 'Sales_Data');
         $tableStyle = new TableStyle();
@@ -55,7 +59,7 @@ class AutoSizeTest extends TestCase
         return $table;
     }
 
-    protected function readColumnSizes(): array
+    private function readColumnSizes(): array
     {
         $columnSizes = [];
         $toColumn = $this->worksheet->getHighestColumn();
diff --git a/tests/PhpSpreadsheetTests/Worksheet/CloneTest.php b/tests/PhpSpreadsheetTests/Worksheet/CloneTest.php
index d722c0554..b66a9dd8d 100644
--- a/tests/PhpSpreadsheetTests/Worksheet/CloneTest.php
+++ b/tests/PhpSpreadsheetTests/Worksheet/CloneTest.php
@@ -52,7 +52,6 @@ class CloneTest extends TestCase
         serialize($sheet1);
     }
 
-    #[\PHPUnit\Framework\Attributes\RunInSeparateProcess]
     public function testSerialize2(): void
     {
         $sheet1 = new Worksheet();