diff --git a/tests/Cf7stgTestCase.php b/tests/Cf7stgTestCase.php
new file mode 100644
index 0000000..e668d3f
--- /dev/null
+++ b/tests/Cf7stgTestCase.php
@@ -0,0 +1,15 @@
+<?php
+declare(strict_types=1);
+
+namespace Cf7stg\Tests;
+
+use PHPUnit\Framework\TestCase;
+
+abstract class Cf7stgTestCase extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+        \Cf7stgWpShimState::reset();
+    }
+}
diff --git a/tests/bootstrap.php b/tests/bootstrap.php
index 5a90ffa..198ab9d 100644
--- a/tests/bootstrap.php
+++ b/tests/bootstrap.php
@@ -20,13 +20,15 @@ final class Cf7stgWpShimState
 {
     /** @var array<string,mixed> */
     public static array $options = [];
-    /** @var array<string,array<int,array{cb:callable,priority:int,accepted_args:int}>> */
+    /** @var array<string,array<int,array{cb:callable,priority:int,accepted_args:int,seq:int}>> */
     public static array $filters = [];
+    public static int $next_seq = 0;
 
     public static function reset(): void
     {
         self::$options = [];
         self::$filters = [];
+        self::$next_seq = 0;
     }
 }
 
@@ -36,7 +38,7 @@ if (!function_exists('apply_filters')) {
             return $value;
         }
         $callbacks = Cf7stgWpShimState::$filters[$tag];
-        usort($callbacks, static fn($a, $b) => $a['priority'] <=> $b['priority']);
+        usort($callbacks, static fn($a, $b) => ($a['priority'] <=> $b['priority']) ?: ($a['seq'] <=> $b['seq']));
         foreach ($callbacks as $f) {
             $cb_args = array_slice(array_merge([$value], $args), 0, $f['accepted_args']);
             $value = call_user_func_array($f['cb'], $cb_args);
@@ -48,7 +50,10 @@ if (!function_exists('apply_filters')) {
 if (!function_exists('add_filter')) {
     function add_filter($tag, $cb, $priority = 10, $accepted_args = 1) {
         Cf7stgWpShimState::$filters[$tag][] = [
-            'cb' => $cb, 'priority' => (int)$priority, 'accepted_args' => (int)$accepted_args,
+            'cb' => $cb,
+            'priority' => (int)$priority,
+            'accepted_args' => (int)$accepted_args,
+            'seq' => Cf7stgWpShimState::$next_seq++,
         ];
         return true;
     }
@@ -56,7 +61,17 @@ if (!function_exists('add_filter')) {
 
 if (!function_exists('remove_all_filters')) {
     function remove_all_filters($tag, $priority = false) {
-        unset(Cf7stgWpShimState::$filters[$tag]);
+        if ($priority === false) {
+            unset(Cf7stgWpShimState::$filters[$tag]);
+            return true;
+        }
+        if (!isset(Cf7stgWpShimState::$filters[$tag])) {
+            return true;
+        }
+        Cf7stgWpShimState::$filters[$tag] = array_values(array_filter(
+            Cf7stgWpShimState::$filters[$tag],
+            static fn($f) => $f['priority'] !== (int)$priority
+        ));
         return true;
     }
 }