Add helper functions for Filter API

app/helpers.php

@@ -65,6 +65,20 @@ if (! function_exists('json')) {
     }
 }
 
+if (! function_exists('add_filter')) {
+    function add_filter($hook, $callback, $priority = 20, $arguments = 1): void
+    {
+        app('eventy')->addFilter($hook, $callback, $priority, $arguments);
+    }
+}
+
+if (! function_exists('apply_filters')) {
+    function apply_filters()
+    {
+        return call_user_func_array([app('eventy'), 'filter'], func_get_args());
+    }
+}
+
 if (! function_exists('bs_footer_extra')) {
     function bs_footer_extra(): string
     {

tests/ServicesTest/FilterTest.php

@@ -0,0 +1,38 @@
+<?php
+
+namespace Tests;
+
+class FilterTest extends TestCase
+{
+    public function testAddFilter()
+    {
+        $this->mock('eventy', function ($mock) {
+            $mock->shouldReceive('addFilter')
+                ->withArgs(function ($hook, $callback) {
+                    $this->assertEquals('my.hook', $hook);
+                    $this->assertEquals('Filtered text', $callback('text'));
+                    return true;
+                })
+                ->once();
+        });
+        add_filter('my.hook', function ($value) {
+            return "Filtered $value";
+        });
+    }
+
+    public function testApplyFilters()
+    {
+        $this->mock('eventy', function ($mock) {
+            $mock->shouldReceive('filter')->withArgs(['my.hook', 'value'])->once();
+        });
+        apply_filters('my.hook', 'value');
+    }
+
+    public function testIntegration()
+    {
+        add_filter('hook.test', function ($value) {
+            return $value.'ed';
+        });
+        $this->assertEquals('tested', apply_filters('hook.test', 'test'));
+    }
+}