diff --git a/.github/workflows/continuous-integration.yml b/.github/workflows/continuous-integration.yml
index 5e5932c..93eb1f0 100644
--- a/.github/workflows/continuous-integration.yml
+++ b/.github/workflows/continuous-integration.yml
@@ -15,14 +15,16 @@ jobs:
     strategy:
       matrix:
         operating-system: ['ubuntu-latest', 'macos-latest']
-        php-version: ['7.2.5', '7.3', '7.4', '8.0']
+        php-version: ['7.2.5', '7.3', '7.4', '8.0', '8.1']
 
     steps:
-      - name: "Checkout"
-        uses: "actions/checkout@v2"
+      - name: Checkout
+        uses: actions/checkout@v2
+        with:
+          fetch-depth: 2
 
-      - name: "Install PHP"
-        uses: "shivammathur/setup-php@v2"
+      - name: Install PHP
+        uses: shivammathur/setup-php@v2
         with:
           php-version: "${{ matrix.php-version }}"
           tools: composer:v2, php-cs-fixer, phpstan
@@ -41,11 +43,17 @@ jobs:
       - name: Install dependencies
         run: composer install --prefer-dist --no-progress --no-suggest
 
-      - name: Test PHPUnit
-        run: ./vendor/bin/phpunit
-
       - name: Test PHP-CS-Fixer
-        run: php-cs-fixer fix --dry-run --diff --no-ansi
+        if: matrix.php-version != '8.1'
+        run: ./vendor/bin/php-cs-fixer fix --dry-run --diff --no-ansi
 
       - name: Test PHPStan
-        run: phpstan analyse
+        run: ./vendor/bin/phpstan analyse
+
+      - name: Test PHPUnit
+        run: ./vendor/bin/phpunit --coverage-clover=coverage.clover
+
+      - name: Upload coverage to Scrutinizer
+        run: |
+          composer global require scrutinizer/ocular
+          ~/.composer/vendor/bin/ocular code-coverage:upload --format=php-clover coverage.clover
diff --git a/Reader/CsvReader.php b/Reader/CsvReader.php
index c693c55..84d3f10 100644
--- a/Reader/CsvReader.php
+++ b/Reader/CsvReader.php
@@ -135,7 +135,7 @@ public function current(): array
     /**
      * {@inheritdoc}
      */
-    public function next()
+    public function next(): void
     {
         $this->iterator->next();
         ++$this->index;
@@ -143,6 +143,8 @@ public function next()
 
     /**
      * {@inheritdoc}
+     *
+     * @return mixed
      */
     public function key()
     {
@@ -152,7 +154,7 @@ public function key()
     /**
      * {@inheritdoc}
      */
-    public function valid()
+    public function valid(): bool
     {
         return $this->iterator->valid();
     }
@@ -160,7 +162,7 @@ public function valid()
     /**
      * {@inheritdoc}
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->iterator->rewind();
 
@@ -175,7 +177,7 @@ public function rewind()
     /**
      * {@inheritdoc}
      */
-    public function count()
+    public function count(): int
     {
         return $this->count;
     }
diff --git a/Reader/ReaderInterface.php b/Reader/ReaderInterface.php
index d99075d..4708a49 100644
--- a/Reader/ReaderInterface.php
+++ b/Reader/ReaderInterface.php
@@ -11,6 +11,8 @@
 
 namespace IQ2i\DataImporter\Reader;
 
+use ReturnTypeWillChange;
+
 interface ReaderInterface extends \Iterator, \Countable
 {
     /**
@@ -41,25 +43,26 @@ public function current(): array;
     /**
      * {@inheritdoc}
      */
-    public function next();
+    public function next(): void;
 
     /**
      * {@inheritdoc}
      */
+    #[ReturnTypeWillChange]
     public function key();
 
     /**
      * {@inheritdoc}
      */
-    public function valid();
+    public function valid(): bool;
 
     /**
      * {@inheritdoc}
      */
-    public function rewind();
+    public function rewind(): void;
 
     /**
      * {@inheritdoc}
      */
-    public function count();
+    public function count(): int;
 }
diff --git a/Reader/XmlReader.php b/Reader/XmlReader.php
index 2dc9e33..b725822 100644
--- a/Reader/XmlReader.php
+++ b/Reader/XmlReader.php
@@ -114,7 +114,7 @@ public function current(): array
     /**
      * {@inheritdoc}
      */
-    public function next()
+    public function next(): void
     {
         $this->iterator->next();
         ++$this->index;
@@ -122,6 +122,8 @@ public function next()
 
     /**
      * {@inheritdoc}
+     *
+     * @return mixed
      */
     public function key()
     {
@@ -131,7 +133,7 @@ public function key()
     /**
      * {@inheritdoc}
      */
-    public function valid()
+    public function valid(): bool
     {
         return $this->iterator->valid();
     }
@@ -139,7 +141,7 @@ public function valid()
     /**
      * {@inheritdoc}
      */
-    public function rewind()
+    public function rewind(): void
     {
         $this->iterator->rewind();
     }
@@ -147,7 +149,7 @@ public function rewind()
     /**
      * {@inheritdoc}
      */
-    public function count()
+    public function count(): int
     {
         return $this->iterator->count();
     }