feat: add ExceptionHandlingTrait and Exceptions::(un)register

app/Views/errors/cli/error_404.php

@@ -1,6 +1,11 @@
 <?php
 
 use CodeIgniter\CLI\CLI;
+use CodeIgniter\Debug\Exceptions;
+
+if (Exceptions::isUsingPhpUnitErrorHandlingInSeparateProcess()) {
+    return;
+}
 
 CLI::error('ERROR: ' . $code);
 CLI::write($message);

app/Views/errors/cli/error_exception.php

@@ -1,6 +1,11 @@
 <?php
 
 use CodeIgniter\CLI\CLI;
+use CodeIgniter\Debug\Exceptions;
+
+if (Exceptions::isUsingPhpUnitErrorHandlingInSeparateProcess()) {
+    return;
+}
 
 // The main Exception
 CLI::write('[' . get_class($exception) . ']', 'light_gray', 'red');

system/CodeIgniter.php

@@ -190,7 +190,7 @@ public function initialize()
         $this->bootstrapEnvironment();
 
         // Setup Exception Handling
-        Services::exceptions()->initialize();
+        Services::exceptions()->register();
 
         // Run this check for manual installations
         if (! is_file(COMPOSER_PATH)) {

system/Debug/Exceptions.php

@@ -104,15 +104,35 @@ public function __construct(ExceptionsConfig $config)
      *
      * @codeCoverageIgnore
      *
+     * @deprecated 4.5.0 Use `register()` instead
+     *
      * @return void
      */
     public function initialize()
+    {
+        $this->register();
+    }
+
+    /**
+     * Responsible for registering the error handler, exception handler,
+     * and shutdown handler.
+     */
+    public function register(): void
     {
         set_exception_handler([$this, 'exceptionHandler']);
         set_error_handler([$this, 'errorHandler']);
         register_shutdown_function([$this, 'shutdownHandler']);
     }
 
+    /**
+     * Unregisters the exception handler and error handler.
+     */
+    public function unregister(): void
+    {
+        restore_exception_handler();
+        restore_error_handler();
+    }
+
     /**
      * Catches any uncaught errors and exceptions, including most Fatal errors
      * (Yay PHP7!). Will log the error, display it if display_errors is on,
@@ -594,6 +614,27 @@ public static function highlightFile(string $file, int $lineNumber, int $lines =
         return '<pre><code>' . $out . '</code></pre>';
     }
 
+    /**
+     * When PHPUnit 9.x is running on a separate process, it registers its
+     * simple error handler through the function '__phpunit_error_handler'.
+     *
+     * This checks whether the test is running in a separate process without
+     * creating a direct dependency on PHPUnit.
+     *
+     * @todo Check if the same function is used on PHPUnit 10.x
+     *
+     * @internal
+     */
+    public static function isUsingPhpUnitErrorHandlingInSeparateProcess(): bool
+    {
+        try {
+            // @phpstan-ignore-next-line
+            return set_error_handler(null) === '__phpunit_error_handler';
+        } finally {
+            restore_error_handler();
+        }
+    }
+
     private static function renderBacktrace(array $backtrace): string
     {
         $backtraces = [];

system/Test/ExceptionHandlingTrait.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace CodeIgniter\Test;
+
+use Config\Services;
+
+/**
+ * Provides utilities for registering and unregistering
+ * of the exception and error handlers.
+ */
+trait ExceptionHandlingTrait
+{
+    protected function enableExceptionHandling(): void
+    {
+        Services::exceptions()->register();
+    }
+
+    protected function disableExceptionHandling(): void
+    {
+        Services::exceptions()->unregister();
+    }
+}

tests/_support/Config/Filters.php

@@ -13,9 +13,14 @@
 
 namespace Tests\Support\Config\Filters;
 
+use CodeIgniter\Debug\Exceptions;
 use Tests\Support\Filters\Customfilter;
 use Tests\Support\Filters\RedirectFilter;
 
+if (Exceptions::isUsingPhpUnitErrorHandlingInSeparateProcess()) {
+    return;
+}
+
 /**
  * @psalm-suppress UndefinedGlobalVariable
  */

tests/system/Debug/ExceptionsTest.php

@@ -20,6 +20,7 @@
 use CodeIgniter\Test\ReflectionHelper;
 use Config\Exceptions as ExceptionsConfig;
 use ErrorException;
+use PHPUnit\Framework\Exception;
 use RuntimeException;
 
 /**
@@ -65,7 +66,7 @@ public function testDeprecationsOnPhp81DoNotThrow(): void
         $config->deprecationLogLevel = 'error';
 
         $this->exception = new Exceptions($config);
-        $this->exception->initialize();
+        $this->exception->register();
 
         // this is only needed for IDEs not to complain that strlen does not accept explicit null
         $maybeNull = PHP_VERSION_ID >= 80100 ? null : 'random string';
@@ -74,11 +75,10 @@ public function testDeprecationsOnPhp81DoNotThrow(): void
             // We test DEPRECATED error, so cannot set `declare(strict_types=1)` in this file.
             strlen($maybeNull);
             $this->assertLogContains('error', '[DEPRECATED] strlen(): ');
-        } catch (ErrorException $e) {
+        } catch (ErrorException) {
             $this->fail('The catch block should not be reached.');
         } finally {
-            restore_error_handler();
-            restore_exception_handler();
+            $this->exception->unregister();
         }
     }
 
@@ -90,13 +90,12 @@ public function testSuppressedDeprecationsAreLogged(): void
         $config->deprecationLogLevel = 'error';
 
         $this->exception = new Exceptions($config);
-        $this->exception->initialize();
+        $this->exception->register();
 
         @trigger_error('Hello! I am a deprecation!', E_USER_DEPRECATED);
         $this->assertLogContains('error', '[DEPRECATED] Hello! I am a deprecation!');
 
-        restore_error_handler();
-        restore_exception_handler();
+        $this->exception->unregister();
     }
 
     public function testDetermineViews(): void
@@ -229,4 +228,15 @@ public function testMaskSensitiveDataTraceDataKey(): void
 
         $this->assertSame('/var/www/CodeIgniter4/app/Controllers/Home.php', $newTrace[0]['file']);
     }
+
+    /**
+     * @runInSeparateProcess
+     */
+    public function testUnregisteringUsesPhpUnitsOwnHandler(): void
+    {
+        $this->exception->unregister();
+
+        $this->expectException(Exception::class); // PHPUnit\Framework\Exception
+        @trigger_error('Hello', E_USER_ERROR);
+    }
 }