Add support for withAnyArgs method for onFilter calls.

docs/usage/mocking-wp-action-and-filter-hooks.md

@@ -103,6 +103,28 @@ final class MyClassTest extends TestCase
 }
 ```
 
+We can also use the `withAnyArgs` method to test that the filter is being applied. This is particularly useful in test cases where we do not care about the arguments but just its return value. This can be done like so:
+
+```php
+use MyPlugin\MyClass;
+use WP_Mock;
+use WP_Mock\Tools\TestCase as TestCase;
+
+final class MyClassTest extends TestCase
+{
+    public function testCanFilterContent() : void 
+    {
+        WP_Mock::onFilter('custom_content_filter')
+            ->withAnyArgs()
+            ->reply('This is filtered');
+
+        $content = (new MyClass())->filterContent();
+
+        $this->assertEquals('This is filtered', $content);
+    }
+}
+```
+
 Alternatively, there is a method `WP_Mock::expectFilter()` that will add a bare assertion that the filter will be applied without changing the value:
 
 ```php

php/WP_Mock/Filter.php

@@ -9,6 +9,9 @@
  */
 class Filter extends Hook
 {
+    /** @var array<mixed> Collection of filter names mapped to random integers. */
+    protected static array $filtersWithAnyArgs = [];
+
     /**
      * Apply the stored filter.
      *
@@ -18,6 +21,10 @@ class Filter extends Hook
      */
     public function apply($args)
     {
+        if (isset(static::$filtersWithAnyArgs[ $this->name ])) {
+            $args = array_values(static::$filtersWithAnyArgs);
+        }
+
         if ($args[0] === null && count($args) === 1) {
             if (isset($this->processors['argsnull'])) {
                 return $this->processors['argsnull']->send();
@@ -42,6 +49,9 @@ public function apply($args)
         return call_user_func_array(array($processors, 'send'), $args);
     }
 
+    /**
+     * @return Filter_Responder
+     */
     protected function new_responder()
     {
         return new Filter_Responder();
@@ -54,6 +64,17 @@ protected function get_strict_mode_message()
     {
         return sprintf('Unexpected use of apply_filters for filter %s', $this->name);
     }
+
+    /**
+     * @return Action_Responder|Filter_Responder|HookedCallbackResponder
+     */
+    public function withAnyArgs()
+    {
+        $random_value = mt_rand();
+        static::$filtersWithAnyArgs[ $this->name ] = $random_value;
+
+        return $this->with($random_value);
+    }
 }
 
 class Filter_Responder

tests/Unit/WP_MockTest.php

@@ -312,4 +312,54 @@ public function testCanGetDeprecatedMethodListener(): void
 
         Mockery::close();
     }
+
+    /**
+     * @covers \WP_Mock::onFilter()
+     *
+     * @runInSeparateProcess
+     * @preserveGlobalState disabled
+     *
+     * @return void
+     * @throws Exception|InvalidArgumentException
+     */
+    public function testOnFilterPasses(): void
+    {
+        WP_Mock::bootstrap();
+
+        /** @phpstan-ignore-next-line */
+        WP_Mock::onFilter('testFilter')
+            ->with('Original value')
+            ->reply('Filtered value');
+
+        $filtered_value = apply_filters('testFilter', 'Original value');
+
+        $this->assertSame('Filtered value', $filtered_value);
+
+        Mockery::close();
+    }
+
+    /**
+     * @covers \WP_Mock::onFilter()
+     *
+     * @runInSeparateProcess
+     * @preserveGlobalState disabled
+     *
+     * @return void
+     * @throws Exception|InvalidArgumentException
+     */
+    public function testOnFilterPassesWithAnyArgs(): void
+    {
+        WP_Mock::bootstrap();
+
+        /** @phpstan-ignore-next-line */
+        WP_Mock::onFilter('testFilter')
+            ->withAnyArgs()
+            ->reply('Filtered value');
+
+        $filtered_value = apply_filters('testFilter', 'Original value');
+
+        $this->assertSame('Filtered value', $filtered_value);
+
+        Mockery::close();
+    }
 }