diff --git a/.php-cs-fixer.php b/.php-cs-fixer.php
index 9171a9a2..6774ea00 100644
--- a/.php-cs-fixer.php
+++ b/.php-cs-fixer.php
@@ -3,7 +3,10 @@
 // This is based on the `@Symfony` rule set documented in `vendor/friendsofphp/php-cs-fixer/doc/ruleSets/Symfony.rst`.
 
 $finder = PhpCsFixer\Finder::create()
-    ->in(__DIR__ . '/lib');
+    ->in([
+        __DIR__ . '/lib',
+        __DIR__ . '/Tests',
+    ]);
 
 return (new PhpCsFixer\Config())
     ->setRules([
diff --git a/Tests/Unit/FinTsTestCase.php b/Tests/Unit/FinTsTestCase.php
index 9cf4fa1d..cf377c12 100644
--- a/Tests/Unit/FinTsTestCase.php
+++ b/Tests/Unit/FinTsTestCase.php
@@ -103,9 +103,8 @@ protected function setUpConnection()
                     + strlen($mockMiddle) + strlen($hnvsd) + strlen($mockSuffix);
                 $newLength = str_pad($newLength, HNHBKv3::NACHRICHTENGROESSE_LENGTH, '0', STR_PAD_LEFT);
                 return $mockPrefix . $newLength . $mockMiddle . $hnvsd . $mockSuffix;
-            } else {
-                return $mockResponse;
             }
+            return $mockResponse;
         });
         return $this->connection;
     }
diff --git a/lib/Fhp/FinTs.php b/lib/Fhp/FinTs.php
index 24f1b6bf..a509328d 100644
--- a/lib/Fhp/FinTs.php
+++ b/lib/Fhp/FinTs.php
@@ -346,7 +346,7 @@ public function execute(BaseAction $action): void
         $message = MessageBuilder::create()->add($requestSegments);
 
         // Add HKTAN for authentication if necessary.
-        if (!($this->getSelectedTanMode() instanceof NoPsd2TanMode)) {
+        if (!$this->getSelectedTanMode() instanceof NoPsd2TanMode) {
             if (($needTanForSegment = $action->getNeedTanForSegment()) !== null) {
                 $message->add(HKTANFactory::createProzessvariante2Step1(
                     $this->requireTanMode(), $this->selectedTanMedium, $needTanForSegment));
@@ -421,11 +421,10 @@ private function processServerResponse(BaseAction $action, Message $response, ?H
                     if ($confirmationRequest->getVerificationResult() === VopVerificationResult::CompletedFullMatch) {
                         // If someone hits this branch in practice, we can implement it.
                         throw new UnsupportedException('Combined VOP match confirmation and TAN request');
-                    } else {
-                        throw new UnexpectedResponseException(
-                            'Unexpected TAN request on VOP result: ' . $confirmationRequest->getVerificationResult()
-                        );
                     }
+                    throw new UnexpectedResponseException(
+                        'Unexpected TAN request on VOP result: ' . $confirmationRequest->getVerificationResult()
+                    );
                 }
             }
         }
@@ -684,7 +683,7 @@ public function pollAction(BaseAction $action): void
     public function confirmVop(BaseAction $action): void
     {
         $vopConfirmationRequest = $action->getVopConfirmationRequest();
-        if (!($vopConfirmationRequest instanceof VopConfirmationRequestImpl)) {
+        if (!$vopConfirmationRequest instanceof VopConfirmationRequestImpl) {
             throw new \InvalidArgumentException('Unexpected type: ' . gettype($vopConfirmationRequest));
         }
         // We need to send the original request again, plus HKVPA as the confirmation.
@@ -697,7 +696,7 @@ public function confirmVop(BaseAction $action): void
             ->add(VopHelper::createHKVPAForConfirmation($vopConfirmationRequest));
 
         // Add HKTAN for authentication if necessary.
-        if (!($this->getSelectedTanMode() instanceof NoPsd2TanMode)) {
+        if (!$this->getSelectedTanMode() instanceof NoPsd2TanMode) {
             if (($needTanForSegment = $action->getNeedTanForSegment()) !== null) {
                 $message->add(HKTANFactory::createProzessvariante2Step1(
                     $this->requireTanMode(), $this->selectedTanMedium, $needTanForSegment));
@@ -930,7 +929,7 @@ private function ensureSynchronized(): void
             // banks that don't support PSD2, we just keep the dummy TAN mode, as they wouldn't even understand 999.
             $oldTanMode = $this->selectedTanMode;
             $oldTanMedium = $this->selectedTanMedium;
-            if (!($this->selectedTanMode instanceof NoPsd2TanMode)) {
+            if (!$this->selectedTanMode instanceof NoPsd2TanMode) {
                 $this->selectedTanMode = null;
             }
             $this->selectedTanMedium = null;
diff --git a/lib/Fhp/Model/StatementOfAccount/Transaction.php b/lib/Fhp/Model/StatementOfAccount/Transaction.php
index af3151fb..7ebb9d7c 100644
--- a/lib/Fhp/Model/StatementOfAccount/Transaction.php
+++ b/lib/Fhp/Model/StatementOfAccount/Transaction.php
@@ -254,9 +254,8 @@ public function getMainDescription(): string
     {
         if (array_key_exists('SVWZ', $this->structuredDescription)) {
             return $this->structuredDescription['SVWZ'];
-        } else {
-            return '';
         }
+        return '';
     }
 
     /**
@@ -266,9 +265,8 @@ public function getEndToEndID(): string
     {
         if (array_key_exists('EREF', $this->structuredDescription)) {
             return $this->structuredDescription['EREF'];
-        } else {
-            return '';
         }
+        return '';
     }
 
     /**
diff --git a/lib/Fhp/Protocol/BPD.php b/lib/Fhp/Protocol/BPD.php
index 5241ab46..fc18f5a3 100644
--- a/lib/Fhp/Protocol/BPD.php
+++ b/lib/Fhp/Protocol/BPD.php
@@ -85,7 +85,7 @@ public function getBankName()
     public function getAllSupportedParameters(string $type): array
     {
         return array_filter($this->parameters[$type] ?? [], function (BaseSegment $segment) {
-            return !($segment instanceof AnonymousSegment);
+            return !$segment instanceof AnonymousSegment;
         });
     }
 
@@ -101,7 +101,7 @@ public function getLatestSupportedParameters(string $type): ?BaseSegment
             return null;
         }
         foreach ($this->parameters[$type] as $segment) {
-            if (!($segment instanceof AnonymousSegment)) {
+            if (!$segment instanceof AnonymousSegment) {
                 return $segment;
             }
         }
diff --git a/lib/Fhp/Protocol/Message.php b/lib/Fhp/Protocol/Message.php
index b4babcfc..853f64dc 100644
--- a/lib/Fhp/Protocol/Message.php
+++ b/lib/Fhp/Protocol/Message.php
@@ -320,11 +320,11 @@ public static function parse(string $rawMessage): Message
         // Message header and footer must always be there, or something went badly wrong.
         $result->header = $segments[0];
         $result->footer = $segments[count($segments) - 1];
-        if (!($result->header instanceof HNHBKv3)) {
+        if (!$result->header instanceof HNHBKv3) {
             $actual = $result->header->getName();
             throw new \InvalidArgumentException("Expected first segment to be HNHBK, but got $actual: $rawMessage");
         }
-        if (!($result->footer instanceof HNHBSv1)) {
+        if (!$result->footer instanceof HNHBSv1) {
             $actual = $result->footer->getName();
             throw new \InvalidArgumentException("Expected last segment to be HNHBS, but got $actual: $rawMessage");
         }
@@ -332,7 +332,7 @@ public static function parse(string $rawMessage): Message
         // Check if there's an encryption header and "encrypted" data.
         // Section B.8 specifies that there are exactly 4 segments: HNHBK, HNVSK, HNVSD, HNHBS.
         if (count($segments) === 4 && $segments[1] instanceof HNVSKv3) {
-            if (!($segments[2] instanceof HNVSDv1)) {
+            if (!$segments[2] instanceof HNVSDv1) {
                 throw new \InvalidArgumentException("Expected third segment to be HNVSD: $rawMessage");
             }
             $result->wrapperSegments = $segments;
diff --git a/lib/Fhp/Segment/BaseSegment.php b/lib/Fhp/Segment/BaseSegment.php
index 3ce4718f..843e6a4d 100644
--- a/lib/Fhp/Segment/BaseSegment.php
+++ b/lib/Fhp/Segment/BaseSegment.php
@@ -123,10 +123,9 @@ public static function parse(string $rawSegment): static
         if (static::class === BaseSegment::class) {
             // Called as BaseSegment::parse(), so we need to determine the right segment type/class.
             return Parser::detectAndParseSegment($rawSegment);
-        } else {
-            // The parse() function was called on the segment subclass itself.
-            return Parser::parseSegment($rawSegment, static::class);
         }
+        // The parse() function was called on the segment subclass itself.
+        return Parser::parseSegment($rawSegment, static::class);
     }
 
     /**
diff --git a/lib/Fhp/Segment/Common/Sdo.php b/lib/Fhp/Segment/Common/Sdo.php
index c43cbbda..2b70587c 100644
--- a/lib/Fhp/Segment/Common/Sdo.php
+++ b/lib/Fhp/Segment/Common/Sdo.php
@@ -36,11 +36,13 @@ public function getAmount(): float
     {
         if ($this->sollHabenKennzeichen === self::CREDIT) {
             return $this->betrag->wert;
-        } elseif ($this->sollHabenKennzeichen === self::DEBIT) {
+        }
+
+        if ($this->sollHabenKennzeichen === self::DEBIT) {
             return -1 * $this->betrag->wert;
-        } else {
-            throw new \InvalidArgumentException("Invalid sollHabenKennzeichen: $this->sollHabenKennzeichen");
         }
+
+        throw new \InvalidArgumentException("Invalid sollHabenKennzeichen: $this->sollHabenKennzeichen");
     }
 
     public function getCurrency(): string
diff --git a/lib/Fhp/Segment/SegmentDescriptor.php b/lib/Fhp/Segment/SegmentDescriptor.php
index 3dc4a973..366eb7ee 100644
--- a/lib/Fhp/Segment/SegmentDescriptor.php
+++ b/lib/Fhp/Segment/SegmentDescriptor.php
@@ -54,7 +54,7 @@ protected function __construct(string $class)
     public function validateObject($obj): void // Override
     {
         parent::validateObject($obj);
-        if (!($obj instanceof BaseSegment)) {
+        if (!$obj instanceof BaseSegment) {
             throw new \InvalidArgumentException('Expected sub-class of BaseSegment, got ' . gettype($obj));
         }
         if ($obj->getName() !== $this->kennung) {
diff --git a/lib/Fhp/Syntax/Parser.php b/lib/Fhp/Syntax/Parser.php
index 72620ac0..018d272b 100644
--- a/lib/Fhp/Syntax/Parser.php
+++ b/lib/Fhp/Syntax/Parser.php
@@ -427,11 +427,13 @@ private static function parseSegmentElement(string $rawElement, ElementDescripto
     {
         if (is_string($descriptor->type)) { // Scalar value / DE
             return static::parseDataElement($rawElement, $descriptor->type);
-        } elseif ($descriptor->type->getName() === Bin::class) {
+        }
+
+        if ($descriptor->type->getName() === Bin::class) {
             return static::parseBinaryBlock($rawElement);
-        } else {
-            return static::parseDeg($rawElement, $descriptor->type->name, $descriptor->optional);
         }
+
+        return static::parseDeg($rawElement, $descriptor->type->name, $descriptor->optional);
     }
 
     /**
diff --git a/lib/Fhp/Syntax/Serializer.php b/lib/Fhp/Syntax/Serializer.php
index c0d64ff3..c66eb829 100644
--- a/lib/Fhp/Syntax/Serializer.php
+++ b/lib/Fhp/Syntax/Serializer.php
@@ -32,18 +32,23 @@ public static function serializeDataElement($value, string $type): string
         if ($value === null) {
             return '';
         }
+
         if ($type === 'int' || $type === 'integer' || $type === 'string') {
             // Convert UTF-8 (PHP's encoding) to ISO-8859-1 (FinTS wire format encoding)
             return static::escape(mb_convert_encoding(strval($value), 'ISO-8859-1', 'UTF-8'));
-        } elseif ($type === 'float') {
+        }
+
+        if ($type === 'float') {
             // Format with fixed 2 decimal places (there has to be some limit, and the specification does not specify
             // one), then trim zeros from the end.
             return rtrim(number_format($value, 2, ',', ''), '0');
-        } elseif ($type === 'bool' || $type === 'boolean') {
+        }
+
+        if ($type === 'bool' || $type === 'boolean') {
             return $value ? 'J' : 'N';
-        } else {
-            throw new \RuntimeException("Unsupported type $type");
         }
+
+        throw new \RuntimeException("Unsupported type $type");
     }
 
     /**
@@ -147,14 +152,18 @@ private static function serializeElement($value, $type, bool $fullySerialize)
     {
         if (is_string($type)) { // Scalar value / DE
             return static::serializeDataElement($value, $type);
-        } elseif ($type->getName() === Bin::class) {
+        }
+
+        if ($type->getName() === Bin::class) {
             /* @var Bin|null $value */
             return $value === null ? '' : $value->toString();
-        } elseif ($fullySerialize) {
+        }
+
+        if ($fullySerialize) {
             return static::serializeDeg($value, DegDescriptor::get($type->name));
-        } else {
-            return static::serializeElements($value, DegDescriptor::get($type->name));
         }
+
+        return static::serializeElements($value, DegDescriptor::get($type->name));
     }
 
     /**