diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8b17217..ca316ab 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -267,4 +267,4 @@ jobs:
         run: composer install --no-progress --prefer-dist --optimize-autoloader
 
       - name: Static Analysis using PHPStan
-        run: phpstan analyse --no-progress src tests
+        run: ./vendor/bin/phpstan analyse -c phpstan.neon --no-progress
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 0000000..fddfd9c
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,9 @@
+parameters:
+    level: 3
+    paths:
+        - src
+        - tests
+    excludePaths:
+        # Exclude these files that are OK
+        - src/Spout/Reader/Common/Creator/ReaderEntityFactory.php
+        - src/Spout/Writer/Common/Creator/WriterEntityFactory.php
diff --git a/src/Spout/Common/Helper/CellTypeHelper.php b/src/Spout/Common/Helper/CellTypeHelper.php
index 97d2e8d..8da35cc 100644
--- a/src/Spout/Common/Helper/CellTypeHelper.php
+++ b/src/Spout/Common/Helper/CellTypeHelper.php
@@ -9,7 +9,7 @@ namespace Box\Spout\Common\Helper;
 class CellTypeHelper
 {
     /**
-     * @param $value
+     * @param mixed|null $value
      * @return bool Whether the given value is considered "empty"
      */
     public static function isEmpty($value)
@@ -18,7 +18,7 @@ class CellTypeHelper
     }
 
     /**
-     * @param $value
+     * @param mixed $value
      * @return bool Whether the given value is a non empty string
      */
     public static function isNonEmptyString($value)
@@ -30,7 +30,7 @@ class CellTypeHelper
      * Returns whether the given value is numeric.
      * A numeric value is from type "integer" or "double" ("float" is not returned by gettype).
      *
-     * @param $value
+     * @param mixed $value
      * @return bool Whether the given value is numeric
      */
     public static function isNumeric($value)
@@ -44,7 +44,7 @@ class CellTypeHelper
      * Returns whether the given value is boolean.
      * "true"/"false" and 0/1 are not booleans.
      *
-     * @param $value
+     * @param mixed $value
      * @return bool Whether the given value is boolean
      */
     public static function isBoolean($value)
@@ -55,7 +55,7 @@ class CellTypeHelper
     /**
      * Returns whether the given value is a DateTime or DateInterval object.
      *
-     * @param $value
+     * @param mixed $value
      * @return bool Whether the given value is a DateTime or DateInterval object
      */
     public static function isDateTimeOrDateInterval($value)
diff --git a/src/Spout/Common/Helper/StringHelper.php b/src/Spout/Common/Helper/StringHelper.php
index 6256b1e..340d65c 100644
--- a/src/Spout/Common/Helper/StringHelper.php
+++ b/src/Spout/Common/Helper/StringHelper.php
@@ -88,7 +88,7 @@ class StringHelper
      * @see https://wiki.php.net/rfc/locale_independent_float_to_string for the changed behavior in PHP8.
      *
      * @param int|float $numericValue
-     * @return string
+     * @return int|float|string
      */
     public function formatNumericValue($numericValue)
     {
diff --git a/src/Spout/Reader/Common/Creator/ReaderFactory.php b/src/Spout/Reader/Common/Creator/ReaderFactory.php
index 6b10175..09ca422 100644
--- a/src/Spout/Reader/Common/Creator/ReaderFactory.php
+++ b/src/Spout/Reader/Common/Creator/ReaderFactory.php
@@ -45,7 +45,7 @@ class ReaderFactory
     /**
      * This creates an instance of the appropriate reader, given the type of the file to be read
      *
-     * @param  string $readerType Type of the reader to instantiate
+     * @param string $readerType Type of the reader to instantiate
      * @throws \Box\Spout\Common\Exception\UnsupportedTypeException
      * @return ReaderInterface
      */
diff --git a/src/Spout/Reader/ODS/Creator/InternalEntityFactory.php b/src/Spout/Reader/ODS/Creator/InternalEntityFactory.php
index cb06ce2..a9d96d6 100644
--- a/src/Spout/Reader/ODS/Creator/InternalEntityFactory.php
+++ b/src/Spout/Reader/ODS/Creator/InternalEntityFactory.php
@@ -105,7 +105,7 @@ class InternalEntityFactory implements InternalEntityFactoryInterface
     }
 
     /**
-     * @param $xmlReader
+     * @param XMLReader $xmlReader
      * @return XMLProcessor
      */
     private function createXMLProcessor($xmlReader)
diff --git a/src/Spout/Reader/ODS/Helper/CellValueFormatter.php b/src/Spout/Reader/ODS/Helper/CellValueFormatter.php
index 77bd3c2..b69dcd6 100644
--- a/src/Spout/Reader/ODS/Helper/CellValueFormatter.php
+++ b/src/Spout/Reader/ODS/Helper/CellValueFormatter.php
@@ -64,7 +64,7 @@ class CellValueFormatter
      * Returns the (unescaped) correctly marshalled, cell value associated to the given XML node.
      * @see http://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#refTable13
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @throws InvalidValueException If the node value is not valid
      * @return string|int|float|bool|\DateTime|\DateInterval The value associated with the cell, empty string if cell's type is void/undefined
      */
@@ -96,7 +96,7 @@ class CellValueFormatter
     /**
      * Returns the cell String value.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return string The value associated with the cell
      */
     protected function formatStringCellValue($node)
@@ -115,7 +115,7 @@ class CellValueFormatter
     }
 
     /**
-     * @param $pNode
+     * @param \DOMNode $pNode
      * @return string
      */
     private function extractTextValueFromNode($pNode)
@@ -159,7 +159,7 @@ class CellValueFormatter
      *
      * @see https://docs.oasis-open.org/office/v1.2/os/OpenDocument-v1.2-os-part1.html#__RefHeading__1415200_253892949
      *
-     * @param \DOMNode $node The XML node representing a whitespace
+     * @param \DOMElement $node The XML node representing a whitespace
      * @return string The corresponding whitespace value
      */
     private function transformWhitespaceNode($node)
@@ -173,7 +173,7 @@ class CellValueFormatter
     /**
      * Returns the cell Numeric value from the given node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return int|float The value associated with the cell
      */
     protected function formatFloatCellValue($node)
@@ -190,7 +190,7 @@ class CellValueFormatter
     /**
      * Returns the cell Boolean value from the given node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return bool The value associated with the cell
      */
     protected function formatBooleanCellValue($node)
@@ -203,7 +203,7 @@ class CellValueFormatter
     /**
      * Returns the cell Date value from the given node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @throws InvalidValueException If the value is not a valid date
      * @return \DateTime|string The value associated with the cell
      */
@@ -234,7 +234,7 @@ class CellValueFormatter
     /**
      * Returns the cell Time value from the given node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @throws InvalidValueException If the value is not a valid time
      * @return \DateInterval|string The value associated with the cell
      */
@@ -265,7 +265,7 @@ class CellValueFormatter
     /**
      * Returns the cell Currency value from the given node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return string The value associated with the cell (e.g. "100 USD" or "9.99 EUR")
      */
     protected function formatCurrencyCellValue($node)
@@ -279,7 +279,7 @@ class CellValueFormatter
     /**
      * Returns the cell Percentage value from the given node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return int|float The value associated with the cell
      */
     protected function formatPercentageCellValue($node)
diff --git a/src/Spout/Reader/ODS/RowIterator.php b/src/Spout/Reader/ODS/RowIterator.php
index 29643b7..f9a0733 100644
--- a/src/Spout/Reader/ODS/RowIterator.php
+++ b/src/Spout/Reader/ODS/RowIterator.php
@@ -56,7 +56,7 @@ class RowIterator implements IteratorInterface
     /** @var Row The currently processed row */
     protected $currentlyProcessedRow;
 
-    /** @var Row Buffer used to store the current row, while checking if there are more rows to read */
+    /** @var Row|null Buffer used to store the current row, while checking if there are more rows to read */
     protected $rowBuffer;
 
     /** @var bool Indicates whether all rows have been read */
@@ -68,7 +68,7 @@ class RowIterator implements IteratorInterface
     /** @var int Row index to be processed next (one-based) */
     protected $nextRowIndexToBeProcessed = 1;
 
-    /** @var Cell Last processed cell (because when reading cell at column N+1, cell N is processed) */
+    /** @var Cell|null Last processed cell (because when reading cell at column N+1, cell N is processed) */
     protected $lastProcessedCell;
 
     /** @var int Number of times the last processed row should be repeated */
@@ -225,6 +225,7 @@ class RowIterator implements IteratorInterface
         $currentNumColumnsRepeated = $this->getNumColumnsRepeatedForCurrentNode($xmlReader);
 
         // NOTE: expand() will automatically decode all XML entities of the child nodes
+        /** @var \DOMElement $node */
         $node = $xmlReader->expand();
         $currentCell = $this->getCell($node);
 
@@ -316,7 +317,7 @@ class RowIterator implements IteratorInterface
     /**
      * Returns the cell with (unescaped) correctly marshalled, cell value associated to the given XML node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return Cell The cell set with the associated with the cell
      */
     protected function getCell($node)
@@ -339,7 +340,7 @@ class RowIterator implements IteratorInterface
      * row data yet (as we still need to apply the "num-columns-repeated" attribute).
      *
      * @param Row $currentRow
-     * @param Cell $lastReadCell The last read cell
+     * @param Cell|null $lastReadCell The last read cell
      * @return bool Whether the row is empty
      */
     protected function isEmptyRow($currentRow, $lastReadCell)
diff --git a/src/Spout/Reader/ODS/SheetIterator.php b/src/Spout/Reader/ODS/SheetIterator.php
index c396d79..b2cb8b8 100644
--- a/src/Spout/Reader/ODS/SheetIterator.php
+++ b/src/Spout/Reader/ODS/SheetIterator.php
@@ -108,6 +108,7 @@ class SheetIterator implements IteratorInterface
         $sheetsVisibility = [];
 
         $this->xmlReader->readUntilNodeFound(self::XML_NODE_AUTOMATIC_STYLES);
+        /** @var \DOMElement $automaticStylesNode */
         $automaticStylesNode = $this->xmlReader->expand();
 
         $tableStyleNodes = $automaticStylesNode->getElementsByTagNameNS(self::XML_STYLE_NAMESPACE, self::XML_NODE_STYLE_TABLE_PROPERTIES);
diff --git a/src/Spout/Reader/ReaderAbstract.php b/src/Spout/Reader/ReaderAbstract.php
index 39b333d..1ef1c20 100644
--- a/src/Spout/Reader/ReaderAbstract.php
+++ b/src/Spout/Reader/ReaderAbstract.php
@@ -53,7 +53,7 @@ abstract class ReaderAbstract implements ReaderInterface
     /**
      * Closes the reader. To be used after reading the file.
      *
-     * @return ReaderAbstract
+     * @return void
      */
     abstract protected function closeReader();
 
diff --git a/src/Spout/Reader/XLSX/Creator/InternalEntityFactory.php b/src/Spout/Reader/XLSX/Creator/InternalEntityFactory.php
index 4dc2dc7..d5ab4c9 100644
--- a/src/Spout/Reader/XLSX/Creator/InternalEntityFactory.php
+++ b/src/Spout/Reader/XLSX/Creator/InternalEntityFactory.php
@@ -152,7 +152,7 @@ class InternalEntityFactory implements InternalEntityFactoryInterface
     }
 
     /**
-     * @param $xmlReader
+     * @param XMLReader $xmlReader
      * @return XMLProcessor
      */
     public function createXMLProcessor($xmlReader)
diff --git a/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php b/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php
index 5fcd794..cf4c383 100644
--- a/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php
+++ b/src/Spout/Reader/XLSX/Helper/CellValueFormatter.php
@@ -66,7 +66,7 @@ class CellValueFormatter
     /**
      * Returns the (unescaped) correctly marshalled, cell value associated to the given XML node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @throws InvalidValueException If the value is not valid
      * @return string|int|float|bool|\DateTime The value associated with the cell
      */
@@ -102,7 +102,7 @@ class CellValueFormatter
     /**
      * Returns the cell's string value from a node's nested value node
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return string The value associated with the cell
      */
     protected function getVNodeValue($node)
@@ -117,7 +117,7 @@ class CellValueFormatter
     /**
      * Returns the cell String value where string is inline.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return string The value associated with the cell
      */
     protected function formatInlineStringCellValue($node)
diff --git a/src/Spout/Reader/XLSX/Manager/SharedStringsCaching/FileBasedStrategy.php b/src/Spout/Reader/XLSX/Manager/SharedStringsCaching/FileBasedStrategy.php
index 60e69b0..9a4142b 100644
--- a/src/Spout/Reader/XLSX/Manager/SharedStringsCaching/FileBasedStrategy.php
+++ b/src/Spout/Reader/XLSX/Manager/SharedStringsCaching/FileBasedStrategy.php
@@ -32,7 +32,7 @@ class FileBasedStrategy implements CachingStrategyInterface
      */
     protected $maxNumStringsPerTempFile;
 
-    /** @var resource Pointer to the last temp file a shared string was written to */
+    /** @var resource|null Pointer to the last temp file a shared string was written to */
     protected $tempFilePointer;
 
     /**
diff --git a/src/Spout/Reader/XLSX/Manager/SharedStringsManager.php b/src/Spout/Reader/XLSX/Manager/SharedStringsManager.php
index 46cbe6d..85d0103 100644
--- a/src/Spout/Reader/XLSX/Manager/SharedStringsManager.php
+++ b/src/Spout/Reader/XLSX/Manager/SharedStringsManager.php
@@ -179,6 +179,7 @@ class SharedStringsManager
         $sharedStringValue = '';
 
         // NOTE: expand() will automatically decode all XML entities of the child nodes
+        /** @var \DOMElement $siNode */
         $siNode = $xmlReader->expand();
         $textNodes = $siNode->getElementsByTagName(self::XML_NODE_T);
 
diff --git a/src/Spout/Reader/XLSX/RowIterator.php b/src/Spout/Reader/XLSX/RowIterator.php
index 93c2b9d..fcb2b88 100644
--- a/src/Spout/Reader/XLSX/RowIterator.php
+++ b/src/Spout/Reader/XLSX/RowIterator.php
@@ -276,6 +276,7 @@ class RowIterator implements IteratorInterface
         $currentColumnIndex = $this->getColumnIndex($xmlReader);
 
         // NOTE: expand() will automatically decode all XML entities of the child nodes
+        /** @var \DOMElement $node */
         $node = $xmlReader->expand();
         $cell = $this->getCell($node);
 
@@ -352,7 +353,7 @@ class RowIterator implements IteratorInterface
     /**
      * Returns the cell with (unescaped) correctly marshalled, cell value associated to the given XML node.
      *
-     * @param \DOMNode $node
+     * @param \DOMElement $node
      * @return Cell The cell set with the associated with the cell
      */
     protected function getCell($node)
diff --git a/src/Spout/Writer/Common/Entity/Worksheet.php b/src/Spout/Writer/Common/Entity/Worksheet.php
index 74c4976..1e496f0 100644
--- a/src/Spout/Writer/Common/Entity/Worksheet.php
+++ b/src/Spout/Writer/Common/Entity/Worksheet.php
@@ -11,7 +11,7 @@ class Worksheet
     /** @var string Path to the XML file that will contain the sheet data */
     private $filePath;
 
-    /** @var resource Pointer to the sheet data file (e.g. xl/worksheets/sheet1.xml) */
+    /** @var resource|null Pointer to the sheet data file (e.g. xl/worksheets/sheet1.xml) */
     private $filePointer;
 
     /** @var Sheet The "external" sheet */
diff --git a/src/Spout/Writer/ODS/Creator/HelperFactory.php b/src/Spout/Writer/ODS/Creator/HelperFactory.php
index e6aa645..cdc5a6a 100644
--- a/src/Spout/Writer/ODS/Creator/HelperFactory.php
+++ b/src/Spout/Writer/ODS/Creator/HelperFactory.php
@@ -30,7 +30,7 @@ class HelperFactory extends \Box\Spout\Common\Creator\HelperFactory
     }
 
     /**
-     * @param $entityFactory
+     * @param InternalEntityFactory $entityFactory
      * @return ZipHelper
      */
     private function createZipHelper($entityFactory)
diff --git a/src/Spout/Writer/ODS/Manager/WorksheetManager.php b/src/Spout/Writer/ODS/Manager/WorksheetManager.php
index 7d7cb0e..e5d51c1 100644
--- a/src/Spout/Writer/ODS/Manager/WorksheetManager.php
+++ b/src/Spout/Writer/ODS/Manager/WorksheetManager.php
@@ -86,7 +86,7 @@ class WorksheetManager implements WorksheetManagerInterface
      * Returns the table XML root node as string.
      *
      * @param Worksheet $worksheet
-     * @return string <table> node as string
+     * @return string "<table>" node as string
      */
     public function getTableElementStartAsString(Worksheet $worksheet)
     {
diff --git a/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php b/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php
index f0ca9d9..4a72b2f 100644
--- a/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php
+++ b/src/Spout/Writer/XLSX/Manager/Style/StyleManager.php
@@ -2,6 +2,7 @@
 
 namespace Box\Spout\Writer\XLSX\Manager\Style;
 
+use Box\Spout\Common\Entity\Style\BorderPart;
 use Box\Spout\Common\Entity\Style\Color;
 use Box\Spout\Common\Entity\Style\Style;
 use Box\Spout\Writer\XLSX\Helper\BorderHelper;
@@ -186,7 +187,7 @@ EOD;
         $content .= '<border><left/><right/><top/><bottom/></border>';
 
         foreach ($registeredBorders as $styleId) {
-            /** @var \Box\Spout\Common\Entity\Style\Style $style */
+            /** @var Style $style */
             $style = $this->styleRegistry->getStyleFromStyleId($styleId);
             $border = $style->getBorder();
             $content .= '<border>';
@@ -196,7 +197,7 @@ EOD;
 
             foreach ($sortOrder as $partName) {
                 if ($border->hasPart($partName)) {
-                    /** @var $part \Box\Spout\Common\Entity\Style\BorderPart */
+                    /** @var BorderPart $part */
                     $part = $border->getPart($partName);
                     $content .= BorderHelper::serializeBorderPart($part);
                 }
diff --git a/src/Spout/Writer/XLSX/Manager/WorksheetManager.php b/src/Spout/Writer/XLSX/Manager/WorksheetManager.php
index 25bb88d..1d90da5 100644
--- a/src/Spout/Writer/XLSX/Manager/WorksheetManager.php
+++ b/src/Spout/Writer/XLSX/Manager/WorksheetManager.php
@@ -240,6 +240,7 @@ EOD;
         } elseif ($cell->isBoolean()) {
             $cellXML .= ' t="b"><v>' . (int) ($cell->getValue()) . '</v></c>';
         } elseif ($cell->isNumeric()) {
+            var_dump($cell);
             $cellXML .= '><v>' . $this->stringHelper->formatNumericValue($cell->getValue()) . '</v></c>';
         } elseif ($cell->isError() && is_string($cell->getValueEvenIfError())) {
             // only writes the error value if it's a string
diff --git a/tests/Spout/Common/Entity/RowTest.php b/tests/Spout/Common/Entity/RowTest.php
index 9aa12f6..bc58499 100644
--- a/tests/Spout/Common/Entity/RowTest.php
+++ b/tests/Spout/Common/Entity/RowTest.php
@@ -7,7 +7,7 @@ use Box\Spout\Common\Entity\Style\Style;
 class RowTest extends \PHPUnit\Framework\TestCase
 {
     /**
-     * @return \PHPUnit_Framework_MockObject_MockObject|Style
+     * @return \PHPUnit\Framework\MockObject\MockObject|Style
      */
     private function getStyleMock()
     {
@@ -15,7 +15,7 @@ class RowTest extends \PHPUnit\Framework\TestCase
     }
 
     /**
-     * @return \PHPUnit_Framework_MockObject_MockObject|Cell
+     * @return \PHPUnit\Framework\MockObject\MockObject|Cell
      */
     private function getCellMock()
     {
diff --git a/tests/Spout/Common/Entity/Style/BorderTest.php b/tests/Spout/Common/Entity/Style/BorderTest.php
index fa1e7ef..bb89af7 100644
--- a/tests/Spout/Common/Entity/Style/BorderTest.php
+++ b/tests/Spout/Common/Entity/Style/BorderTest.php
@@ -113,7 +113,7 @@ class BorderTest extends TestCase
                     $border->addPart($borderPart);
                     $this->assertCount(1, $border->getParts());
 
-                    /** @var $part BorderPart */
+                    /** @var BorderPart $part */
                     $part = $border->getParts()[$allowedName];
 
                     $this->assertEquals($allowedStyle, $part->getStyle());
diff --git a/tests/Spout/Common/Helper/EncodingHelperTest.php b/tests/Spout/Common/Helper/EncodingHelperTest.php
index 8d3c158..ad4dd91 100644
--- a/tests/Spout/Common/Helper/EncodingHelperTest.php
+++ b/tests/Spout/Common/Helper/EncodingHelperTest.php
@@ -68,15 +68,15 @@ class EncodingHelperTest extends TestCase
         $this->expectException(EncodingConversionException::class);
 
         $helperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\GlobalFunctionsHelper')
-                        ->setMethods(['iconv', 'mb_convert_encoding'])
+                        ->onlyMethods(['iconv', 'mb_convert_encoding'])
                         ->getMock();
         $helperStub->method('iconv')->willReturn(false);
         $helperStub->method('mb_convert_encoding')->willReturn(false);
 
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->setConstructorArgs([$helperStub])
-                        ->setMethods(['canUseIconv', 'canUseMbString'])
+                        ->onlyMethods(['canUseIconv', 'canUseMbString'])
                         ->getMock();
         $encodingHelperStub->method('canUseIconv')->willReturn($shouldUseIconv);
         $encodingHelperStub->method('canUseMbString')->willReturn(true);
@@ -91,10 +91,10 @@ class EncodingHelperTest extends TestCase
     {
         $this->expectException(EncodingConversionException::class);
 
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->disableOriginalConstructor()
-                        ->setMethods(['canUseIconv', 'canUseMbString'])
+                        ->onlyMethods(['canUseIconv', 'canUseMbString'])
                         ->getMock();
         $encodingHelperStub->method('canUseIconv')->willReturn(false);
         $encodingHelperStub->method('canUseMbString')->willReturn(false);
@@ -110,10 +110,10 @@ class EncodingHelperTest extends TestCase
      */
     public function testAttemptConversionToUTF8ShouldReturnReencodedString($shouldUseIconv)
     {
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->setConstructorArgs([new GlobalFunctionsHelper()])
-                        ->setMethods(['canUseIconv', 'canUseMbString'])
+                        ->onlyMethods(['canUseIconv', 'canUseMbString'])
                         ->getMock();
         $encodingHelperStub->method('canUseIconv')->willReturn($shouldUseIconv);
         $encodingHelperStub->method('canUseMbString')->willReturn(true);
@@ -129,10 +129,10 @@ class EncodingHelperTest extends TestCase
      */
     public function testAttemptConversionToUTF8ShouldBeNoopWhenTargetIsUTF8()
     {
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->disableOriginalConstructor()
-                        ->setMethods(['canUseIconv'])
+                        ->onlyMethods(['canUseIconv'])
                         ->getMock();
         $encodingHelperStub->expects($this->never())->method('canUseIconv');
 
@@ -151,15 +151,15 @@ class EncodingHelperTest extends TestCase
         $this->expectException(EncodingConversionException::class);
 
         $helperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\GlobalFunctionsHelper')
-                        ->setMethods(['iconv', 'mb_convert_encoding'])
+                        ->onlyMethods(['iconv', 'mb_convert_encoding'])
                         ->getMock();
         $helperStub->method('iconv')->willReturn(false);
         $helperStub->method('mb_convert_encoding')->willReturn(false);
 
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->setConstructorArgs([$helperStub])
-                        ->setMethods(['canUseIconv', 'canUseMbString'])
+                        ->onlyMethods(['canUseIconv', 'canUseMbString'])
                         ->getMock();
         $encodingHelperStub->method('canUseIconv')->willReturn($shouldUseIconv);
         $encodingHelperStub->method('canUseMbString')->willReturn(true);
@@ -174,10 +174,10 @@ class EncodingHelperTest extends TestCase
     {
         $this->expectException(EncodingConversionException::class);
 
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->disableOriginalConstructor()
-                        ->setMethods(['canUseIconv', 'canUseMbString'])
+                        ->onlyMethods(['canUseIconv', 'canUseMbString'])
                         ->getMock();
         $encodingHelperStub->method('canUseIconv')->willReturn(false);
         $encodingHelperStub->method('canUseMbString')->willReturn(false);
@@ -193,10 +193,10 @@ class EncodingHelperTest extends TestCase
      */
     public function testAttemptConversionFromUTF8ShouldReturnReencodedString($shouldUseIconv)
     {
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->setConstructorArgs([new GlobalFunctionsHelper()])
-                        ->setMethods(['canUseIconv', 'canUseMbString'])
+                        ->onlyMethods(['canUseIconv', 'canUseMbString'])
                         ->getMock();
         $encodingHelperStub->method('canUseIconv')->willReturn($shouldUseIconv);
         $encodingHelperStub->method('canUseMbString')->willReturn(true);
@@ -212,10 +212,10 @@ class EncodingHelperTest extends TestCase
      */
     public function testAttemptConversionFromUTF8ShouldBeNoopWhenTargetIsUTF8()
     {
-        /** @var EncodingHelper $encodingHelperStub */
+        /** @var EncodingHelper|\PHPUnit\Framework\MockObject\MockObject $encodingHelperStub */
         $encodingHelperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\EncodingHelper')
                         ->disableOriginalConstructor()
-                        ->setMethods(['canUseIconv'])
+                        ->onlyMethods(['canUseIconv'])
                         ->getMock();
         $encodingHelperStub->expects($this->never())->method('canUseIconv');
 
diff --git a/tests/Spout/Common/Helper/FileSystemHelperTest.php b/tests/Spout/Common/Helper/FileSystemHelperTest.php
index 7eb0183..0eb314e 100644
--- a/tests/Spout/Common/Helper/FileSystemHelperTest.php
+++ b/tests/Spout/Common/Helper/FileSystemHelperTest.php
@@ -10,7 +10,7 @@ use PHPUnit\Framework\TestCase;
  */
 class FileSystemHelperTest extends TestCase
 {
-    /** @var \Box\Spout\Writer\XLSX\Helper\FileSystemHelper */
+    /** @var FileSystemHelper */
     protected $fileSystemHelper;
 
     /**
diff --git a/tests/Spout/Reader/CSV/ReaderTest.php b/tests/Spout/Reader/CSV/ReaderTest.php
index 1d092f0..78f1d42 100644
--- a/tests/Spout/Reader/CSV/ReaderTest.php
+++ b/tests/Spout/Reader/CSV/ReaderTest.php
@@ -47,9 +47,9 @@ class ReaderTest extends TestCase
     {
         $this->expectException(IOException::class);
 
-        /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper|\PHPUnit_Framework_MockObject_MockObject $helperStub */
+        /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper|\PHPUnit\Framework\MockObject\MockObject $helperStub */
         $helperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\GlobalFunctionsHelper')
-                        ->setMethods(['is_readable'])
+                        ->onlyMethods(['is_readable'])
                         ->getMock();
         $helperStub->method('is_readable')->willReturn(false);
 
@@ -66,9 +66,9 @@ class ReaderTest extends TestCase
     {
         $this->expectException(IOException::class);
 
-        /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper|\PHPUnit_Framework_MockObject_MockObject $helperStub */
+        /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper|\PHPUnit\Framework\MockObject\MockObject $helperStub */
         $helperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\GlobalFunctionsHelper')
-                        ->setMethods(['fopen'])
+                        ->onlyMethods(['fopen'])
                         ->getMock();
         $helperStub->method('fopen')->willReturn(false);
 
@@ -304,9 +304,9 @@ class ReaderTest extends TestCase
         $allRows = [];
         $resourcePath = $this->getResourcePath($fileName);
 
-        /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper|\PHPUnit_Framework_MockObject_MockObject $helperStub */
+        /** @var \Box\Spout\Common\Helper\GlobalFunctionsHelper|\PHPUnit\Framework\MockObject\MockObject $helperStub */
         $helperStub = $this->getMockBuilder('\Box\Spout\Common\Helper\GlobalFunctionsHelper')
-                        ->setMethods(['function_exists'])
+                        ->onlyMethods(['function_exists'])
                         ->getMock();
 
         $returnValueMap = [
diff --git a/tests/Spout/Reader/XLSX/Manager/SharedStringsCaching/CachingStrategyFactoryTest.php b/tests/Spout/Reader/XLSX/Manager/SharedStringsCaching/CachingStrategyFactoryTest.php
index 6216b40..5b75cbd 100644
--- a/tests/Spout/Reader/XLSX/Manager/SharedStringsCaching/CachingStrategyFactoryTest.php
+++ b/tests/Spout/Reader/XLSX/Manager/SharedStringsCaching/CachingStrategyFactoryTest.php
@@ -36,11 +36,11 @@ class CachingStrategyFactoryTest extends TestCase
      */
     public function testCreateBestCachingStrategy($sharedStringsUniqueCount, $memoryLimitInKB, $expectedStrategyClassName)
     {
-        /** @var CachingStrategyFactory|\PHPUnit_Framework_MockObject_MockObject $factoryStub */
+        /** @var CachingStrategyFactory|\PHPUnit\Framework\MockObject\MockObject $factoryStub */
         $factoryStub = $this
             ->getMockBuilder('\Box\Spout\Reader\XLSX\Manager\SharedStringsCaching\CachingStrategyFactory')
             ->disableOriginalConstructor()
-            ->setMethods(['getMemoryLimitInKB'])
+            ->onlyMethods(['getMemoryLimitInKB'])
             ->getMock();
 
         $factoryStub->method('getMemoryLimitInKB')->willReturn($memoryLimitInKB);
@@ -84,11 +84,11 @@ class CachingStrategyFactoryTest extends TestCase
      */
     public function testGetMemoryLimitInKB($memoryLimitFormatted, $expectedMemoryLimitInKB)
     {
-        /** @var CachingStrategyFactory|\PHPUnit_Framework_MockObject_MockObject $factoryStub */
+        /** @var CachingStrategyFactory|\PHPUnit\Framework\MockObject\MockObject $factoryStub */
         $factoryStub = $this
             ->getMockBuilder('\Box\Spout\Reader\XLSX\Manager\SharedStringsCaching\CachingStrategyFactory')
             ->disableOriginalConstructor()
-            ->setMethods(['getMemoryLimitFromIni'])
+            ->onlyMethods(['getMemoryLimitFromIni'])
             ->getMock();
 
         $factoryStub->method('getMemoryLimitFromIni')->willReturn($memoryLimitFormatted);
diff --git a/tests/Spout/Reader/XLSX/Manager/SharedStringsManagerTest.php b/tests/Spout/Reader/XLSX/Manager/SharedStringsManagerTest.php
index f344b35..4c3e512 100644
--- a/tests/Spout/Reader/XLSX/Manager/SharedStringsManagerTest.php
+++ b/tests/Spout/Reader/XLSX/Manager/SharedStringsManagerTest.php
@@ -19,7 +19,7 @@ class SharedStringsManagerTest extends TestCase
 {
     use TestUsingResource;
 
-    /** @var SharedStringsManager */
+    /** @var SharedStringsManager|null */
     private $sharedStringsManager;
 
     /**
diff --git a/tests/Spout/Reader/XLSX/Manager/StyleManagerTest.php b/tests/Spout/Reader/XLSX/Manager/StyleManagerTest.php
index 794f4bc..7a98f0e 100644
--- a/tests/Spout/Reader/XLSX/Manager/StyleManagerTest.php
+++ b/tests/Spout/Reader/XLSX/Manager/StyleManagerTest.php
@@ -21,10 +21,10 @@ class StyleManagerTest extends TestCase
         $workbookRelationshipsManager = $this->createMock(WorkbookRelationshipsManager::class);
         $workbookRelationshipsManager->method('hasStylesXMLFile')->willReturn(true);
 
-        /** @var StyleManager $styleManager */
+        /** @var StyleManager|\PHPUnit\Framework\MockObject\MockObject $styleManager */
         $styleManager = $this->getMockBuilder('\Box\Spout\Reader\XLSX\Manager\StyleManager')
                              ->setConstructorArgs(['/path/to/file.xlsx', $workbookRelationshipsManager, $entityFactory])
-                             ->setMethods(['getCustomNumberFormats', 'getStylesAttributes'])
+                             ->onlyMethods(['getCustomNumberFormats', 'getStylesAttributes'])
                              ->getMock();
 
         $styleManager->method('getStylesAttributes')->willReturn($styleAttributes);
diff --git a/tests/Spout/ReflectionHelper.php b/tests/Spout/ReflectionHelper.php
index d958df0..e046046 100644
--- a/tests/Spout/ReflectionHelper.php
+++ b/tests/Spout/ReflectionHelper.php
@@ -95,7 +95,6 @@ class ReflectionHelper
      *
      * @param object $object
      * @param string $methodName
-     * @param *mixed|null $params
      *
      * @return mixed|null
      */
diff --git a/tests/Spout/Writer/ODS/WriterTest.php b/tests/Spout/Writer/ODS/WriterTest.php
index dc86f7c..1d1ff44 100644
--- a/tests/Spout/Writer/ODS/WriterTest.php
+++ b/tests/Spout/Writer/ODS/WriterTest.php
@@ -348,6 +348,7 @@ class WriterTest extends TestCase
         $fileName = 'test_add_row_should_use_number_columns_repeated.ods';
         $this->writeToODSFile($this->createRowsFromValues([$dataRow]), $fileName);
 
+        /** @var \DOMElement $sheetXmlNode */
         $sheetXmlNode = $this->getSheetXmlNode($fileName, 1);
         $tableCellNodes = $sheetXmlNode->getElementsByTagName('table-cell');
 
diff --git a/tests/Spout/Writer/ODS/WriterWithStyleTest.php b/tests/Spout/Writer/ODS/WriterWithStyleTest.php
index 75177da..3c7a6fd 100644
--- a/tests/Spout/Writer/ODS/WriterWithStyleTest.php
+++ b/tests/Spout/Writer/ODS/WriterWithStyleTest.php
@@ -88,6 +88,7 @@ class WriterWithStyleTest extends TestCase
         $this->assertCount(3, $cellStyleElements, 'There should be 3 separate cell styles, including the default one.');
 
         // Second font should contain data from the first created style
+        /** @var \DOMElement $customFont1Element */
         $customFont1Element = $cellStyleElements[1];
         $this->assertFirstChildHasAttributeEquals('bold', $customFont1Element, 'text-properties', 'fo:font-weight');
         $this->assertFirstChildHasAttributeEquals('italic', $customFont1Element, 'text-properties', 'fo:font-style');
@@ -95,6 +96,7 @@ class WriterWithStyleTest extends TestCase
         $this->assertFirstChildHasAttributeEquals('solid', $customFont1Element, 'text-properties', 'style:text-line-through-style');
 
         // Third font should contain data from the second created style
+        /** @var \DOMElement $customFont2Element */
         $customFont2Element = $cellStyleElements[2];
         $this->assertFirstChildHasAttributeEquals('15pt', $customFont2Element, 'text-properties', 'fo:font-size');
         $this->assertFirstChildHasAttributeEquals('#' . Color::RED, $customFont2Element, 'text-properties', 'fo:color');
@@ -397,7 +399,7 @@ class WriterWithStyleTest extends TestCase
 
     /**
      * @param string $fileName
-     * @return \DOMNode[]
+     * @return \DOMElement[]
      */
     private function getCellElementsFromContentXmlFile($fileName)
     {
@@ -410,7 +412,9 @@ class WriterWithStyleTest extends TestCase
 
         while ($xmlReader->read()) {
             if ($xmlReader->isPositionedOnStartingNode('table:table-cell') && $xmlReader->getAttribute('office:value-type') !== null) {
-                $cellElements[] = $xmlReader->expand();
+                /** @var \DOMElement $cellElement */
+                $cellElement = $xmlReader->expand();
+                $cellElements[] = $cellElement;
             }
         }
 
@@ -421,7 +425,7 @@ class WriterWithStyleTest extends TestCase
 
     /**
      * @param string $fileName
-     * @return \DOMNode[]
+     * @return \DOMElement[]
      */
     private function getCellStyleElementsFromContentXmlFile($fileName)
     {
@@ -434,7 +438,9 @@ class WriterWithStyleTest extends TestCase
 
         while ($xmlReader->read()) {
             if ($xmlReader->isPositionedOnStartingNode('style:style') && $xmlReader->getAttribute('style:family') === 'table-cell') {
-                $cellStyleElements[] = $xmlReader->expand();
+                /** @var \DOMElement $cellStyleElement */
+                $cellStyleElement = $xmlReader->expand();
+                $cellStyleElements[] = $cellStyleElement;
             }
         }
 
@@ -446,7 +452,7 @@ class WriterWithStyleTest extends TestCase
     /**
      * @param string $fileName
      * @param string $section
-     * @return \DomNode
+     * @return \DOMElement
      */
     private function getXmlSectionFromStylesXmlFile($fileName, $section)
     {
@@ -456,12 +462,15 @@ class WriterWithStyleTest extends TestCase
         $xmlReader->openFileInZip($resourcePath, 'styles.xml');
         $xmlReader->readUntilNodeFound($section);
 
-        return $xmlReader->expand();
+        /** @var \DOMElement $element */
+        $element = $xmlReader->expand();
+
+        return $element;
     }
 
     /**
      * @param string $expectedValue
-     * @param \DOMNode $parentElement
+     * @param \DOMElement $parentElement
      * @param string $childTagName
      * @param string $attributeName
      * @return void
diff --git a/tests/Spout/Writer/XLSX/Manager/Style/StyleManagerTest.php b/tests/Spout/Writer/XLSX/Manager/Style/StyleManagerTest.php
index 3bb0f42..1c21cc3 100644
--- a/tests/Spout/Writer/XLSX/Manager/Style/StyleManagerTest.php
+++ b/tests/Spout/Writer/XLSX/Manager/Style/StyleManagerTest.php
@@ -40,7 +40,7 @@ class StyleManagerTest extends TestCase
     {
         $styleRegistryMock = $this->getMockBuilder(StyleRegistry::class)
                                 ->disableOriginalConstructor()
-                                ->setMethods(['getFillIdForStyleId', 'getBorderIdForStyleId'])
+                                ->onlyMethods(['getFillIdForStyleId', 'getBorderIdForStyleId'])
                                 ->getMock();
 
         $styleRegistryMock
diff --git a/tests/Spout/Writer/XLSX/WriterPerfTest.php b/tests/Spout/Writer/XLSX/WriterPerfTest.php
index 66ff337..a0f6e90 100644
--- a/tests/Spout/Writer/XLSX/WriterPerfTest.php
+++ b/tests/Spout/Writer/XLSX/WriterPerfTest.php
@@ -102,7 +102,7 @@ class WriterPerfTest extends TestCase
 
     /**
      * @param string $filePath
-     * @return string
+     * @return int
      */
     private function getLasRowNumberForFile($filePath)
     {
diff --git a/tests/Spout/Writer/XLSX/WriterWithStyleTest.php b/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
index 2571df4..7237039 100644
--- a/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
+++ b/tests/Spout/Writer/XLSX/WriterWithStyleTest.php
@@ -92,6 +92,7 @@ class WriterWithStyleTest extends TestCase
         $this->assertEquals(3, $fontElements->length, 'There should be 3 associated "font" elements, including the default one.');
 
         // First font should be the default one
+        /** @var \DOMElement $defaultFontElement */
         $defaultFontElement = $fontElements->item(0);
         $this->assertChildrenNumEquals(3, $defaultFontElement, 'The default font should only have 3 properties.');
         $this->assertFirstChildHasAttributeEquals((string) OptionsManager::DEFAULT_FONT_SIZE, $defaultFontElement, 'sz', 'val');
@@ -99,6 +100,7 @@ class WriterWithStyleTest extends TestCase
         $this->assertFirstChildHasAttributeEquals(OptionsManager::DEFAULT_FONT_NAME, $defaultFontElement, 'name', 'val');
 
         // Second font should contain data from the first created style
+        /** @var \DOMElement $secondFontElement */
         $secondFontElement = $fontElements->item(1);
         $this->assertChildrenNumEquals(7, $secondFontElement, 'The font should only have 7 properties (4 custom styles + 3 default styles).');
         $this->assertChildExists($secondFontElement, 'b');
@@ -110,6 +112,7 @@ class WriterWithStyleTest extends TestCase
         $this->assertFirstChildHasAttributeEquals(OptionsManager::DEFAULT_FONT_NAME, $secondFontElement, 'name', 'val');
 
         // Third font should contain data from the second created style
+        /** @var \DOMElement $thirdFontElement */
         $thirdFontElement = $fontElements->item(2);
         $this->assertChildrenNumEquals(3, $thirdFontElement, 'The font should only have 3 properties.');
         $this->assertFirstChildHasAttributeEquals('15', $thirdFontElement, 'sz', 'val');
@@ -394,10 +397,14 @@ class WriterWithStyleTest extends TestCase
             '3 cell xfs present - a default one and two custom ones'
         );
 
-        $firstCustomId = $styleXfsElements->childNodes->item(1)->getAttribute('fillId');
+        /** @var \DOMElement $styleXfsElementChild1 */
+        $styleXfsElementChild1 = $styleXfsElements->childNodes->item(1);
+        $firstCustomId = $styleXfsElementChild1->getAttribute('fillId');
         $this->assertEquals(2, (int) $firstCustomId, 'The first custom fill id should have the index 2');
 
-        $secondCustomId = $styleXfsElements->childNodes->item(2)->getAttribute('fillId');
+        /** @var \DOMElement $styleXfsElementChild2 */
+        $styleXfsElementChild2 = $styleXfsElements->childNodes->item(2);
+        $secondCustomId = $styleXfsElementChild2->getAttribute('fillId');
         $this->assertEquals(2, (int) $secondCustomId, 'The second custom fill id should have the index 2');
     }
 
@@ -607,7 +614,7 @@ class WriterWithStyleTest extends TestCase
     /**
      * @param string $fileName
      * @param string $section
-     * @return \DomElement
+     * @return \DOMElement
      */
     private function getXmlSectionFromStylesXmlFile($fileName, $section)
     {
@@ -617,6 +624,7 @@ class WriterWithStyleTest extends TestCase
         $xmlReader->openFileInZip($resourcePath, 'xl/styles.xml');
         $xmlReader->readUntilNodeFound($section);
 
+        /** @var \DOMElement $xmlSection */
         $xmlSection = $xmlReader->expand();
 
         $xmlReader->close();
@@ -626,7 +634,7 @@ class WriterWithStyleTest extends TestCase
 
     /**
      * @param string $fileName
-     * @return \DOMNode[]
+     * @return \DOMElement[]
      */
     private function getCellElementsFromSheetXmlFile($fileName)
     {
@@ -639,7 +647,9 @@ class WriterWithStyleTest extends TestCase
 
         while ($xmlReader->read()) {
             if ($xmlReader->isPositionedOnStartingNode('c')) {
-                $cellElements[] = $xmlReader->expand();
+                /** @var \DOMElement $cellElement */
+                $cellElement = $xmlReader->expand();
+                $cellElements[] = $cellElement;
             }
         }
 
@@ -650,7 +660,7 @@ class WriterWithStyleTest extends TestCase
 
     /**
      * @param string $expectedValue
-     * @param \DOMNode $parentElement
+     * @param \DOMElement $parentElement
      * @param string $childTagName
      * @param string $attributeName
      * @return void
@@ -662,7 +672,7 @@ class WriterWithStyleTest extends TestCase
 
     /**
      * @param int $expectedNumber
-     * @param \DOMNode $parentElement
+     * @param \DOMElement $parentElement
      * @param string $message
      * @return void
      */
@@ -672,7 +682,7 @@ class WriterWithStyleTest extends TestCase
     }
 
     /**
-     * @param \DOMNode $parentElement
+     * @param \DOMElement $parentElement
      * @param string $childTagName
      * @return void
      */