diff --git a/.github/workflows/run-tests.yml b/.github/workflows/run-tests.yml
index 87def26..0142f03 100644
--- a/.github/workflows/run-tests.yml
+++ b/.github/workflows/run-tests.yml
@@ -13,7 +13,7 @@ jobs:
       fail-fast: true
       matrix:
         os: [ubuntu-latest]
-        php: [8.2, 8.1, 8.0, 7.4]
+        php: [8.4, 8.2, 8.1, 8.0, 7.4]
 
     name: P${{ matrix.php }} - ${{ matrix.stability }} - ${{ matrix.os }}
 
@@ -36,7 +36,12 @@ jobs:
       - name: Install dependencies
         run: composer update --prefer-stable --prefer-dist --no-interaction
 
-      - name: Execute tests
+      - name: Execute tests (PHP 8.4 -  unit suite only)
+        if: matrix.php == '8.4'
+        run: ./vendor/bin/phpunit --testsuite Unit
+
+      - name: Execute tests (older PHP - full suite with snapshots)
+        if: matrix.php != '8.4'
         run: ./vendor/bin/phpunit --coverage-clover clover.xml -d --without-creating-snapshots
 
       - name: Upload coverage to Codecov
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 172df2a..d164dce 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -22,6 +22,11 @@
         <testsuite name="Permafrost Test Suite">
             <directory>tests</directory>
         </testsuite>
+        <testsuite name="Unit">
+            <directory>tests</directory>
+            <exclude>tests/SearcherTest.php</exclude>
+            <exclude>tests/Results/SearchResultTest.php</exclude>
+        </testsuite>
     </testsuites>
     <coverage>
         <include>
diff --git a/src/Support/Arr.php b/src/Support/Arr.php
index be1f4e0..eab10c0 100644
--- a/src/Support/Arr.php
+++ b/src/Support/Arr.php
@@ -119,7 +119,7 @@ public static function exists($array, $key): bool
      * @param  mixed  $default
      * @return mixed
      */
-    public static function first($array, callable $callback = null, $default = null)
+    public static function first($array, ?callable $callback = null, $default = null)
     {
         if (is_null($callback)) {
             if (empty($array)) {
@@ -148,7 +148,7 @@ public static function first($array, callable $callback = null, $default = null)
      * @param  mixed  $default
      * @return mixed
      */
-    public static function last(array $array, callable $callback = null, $default = null)
+    public static function last(array $array, ?callable $callback = null, $default = null)
     {
         if (is_null($callback)) {
             return empty($array) ? val($default) : end($array);
diff --git a/src/Support/Collections/Collection.php b/src/Support/Collections/Collection.php
index 9b80ff7..91925f6 100644
--- a/src/Support/Collections/Collection.php
+++ b/src/Support/Collections/Collection.php
@@ -37,7 +37,7 @@ public function each(callable $callback): self
         return $this;
     }
 
-    public function filter(callable $callback = null): self
+    public function filter(?callable $callback = null): self
     {
         if ($callback) {
             return new static(Arr::where($this->items, $callback));
@@ -53,7 +53,7 @@ public function filter(callable $callback = null): self
      * @param  mixed  $default
      * @return mixed
      */
-    public function first(callable $callback = null, $default = null)
+    public function first(?callable $callback = null, $default = null)
     {
         return Arr::first($this->items, $callback, $default);
     }
diff --git a/src/Support/VirtualFile.php b/src/Support/VirtualFile.php
index 09bd3c2..9ee657f 100644
--- a/src/Support/VirtualFile.php
+++ b/src/Support/VirtualFile.php
@@ -18,7 +18,7 @@ public function __destruct()
 
     public function unlink()
     {
-        if (! strpos(dirname($this->path), sys_get_temp_dir())) {
+        if (strpos(dirname($this->path), sys_get_temp_dir()) === false) {
             return;
         }