fix: preserve enclosing stream filter when using MockInputOutput

system/Test/Filters/CITestStreamFilter.php

@@ -92,6 +92,22 @@ public static function removeOutputFilter(): void
         self::removeFilter(self::$out);
     }
 
+    /**
+     * Whether an output filter is currently attached to STDOUT.
+     */
+    public static function hasOutputFilter(): bool
+    {
+        return self::$out !== null;
+    }
+
+    /**
+     * Whether an error filter is currently attached to STDERR.
+     */
+    public static function hasErrorFilter(): bool
+    {
+        return self::$err !== null;
+    }
+
     /**
      * @param resource|null $stream
      *

system/Test/Mock/MockInputOutput.php

@@ -35,6 +35,16 @@ final class MockInputOutput extends InputOutput
      */
     private array $outputs = [];
 
+    /**
+     * Snapshot of the shared CITestStreamFilter state captured before this
+     * object attaches its own filters, restored once it is done. Lets a test
+     * combine MockInputOutput with an enclosing StreamFilterTrait without the
+     * latter's filters being torn down.
+     *
+     * @var array{output: bool, error: bool, buffer: string}|null
+     */
+    private ?array $priorFilterState = null;
+
     /**
      * Sets user inputs.
      *
@@ -88,6 +98,12 @@ public function getOutputs(): array
 
     private function addStreamFilters(): void
     {
+        $this->priorFilterState = [
+            'output' => CITestStreamFilter::hasOutputFilter(),
+            'error'  => CITestStreamFilter::hasErrorFilter(),
+            'buffer' => CITestStreamFilter::$buffer,
+        ];
+
         CITestStreamFilter::registration();
         CITestStreamFilter::addOutputFilter();
         CITestStreamFilter::addErrorFilter();
@@ -97,6 +113,22 @@ private function removeStreamFilters(): void
     {
         CITestStreamFilter::removeOutputFilter();
         CITestStreamFilter::removeErrorFilter();
+
+        if ($this->priorFilterState === null) {
+            return;
+        }
+
+        CITestStreamFilter::$buffer = $this->priorFilterState['buffer'];
+
+        if ($this->priorFilterState['output']) {
+            CITestStreamFilter::addOutputFilter();
+        }
+
+        if ($this->priorFilterState['error']) {
+            CITestStreamFilter::addErrorFilter();
+        }
+
+        $this->priorFilterState = null;
     }
 
     public function input(?string $prefix = null): string

tests/system/Test/Mock/MockInputOutputTest.php

@@ -0,0 +1,68 @@
+<?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\Mock;
+
+use CodeIgniter\CLI\CLI;
+use CodeIgniter\Test\CIUnitTestCase;
+use CodeIgniter\Test\StreamFilterTrait;
+use PHPUnit\Framework\Attributes\Group;
+
+/**
+ * @internal
+ */
+#[Group('Others')]
+final class MockInputOutputTest extends CIUnitTestCase
+{
+    use StreamFilterTrait;
+
+    protected function tearDown(): void
+    {
+        parent::tearDown();
+
+        CLI::resetInputOutput();
+    }
+
+    public function testFwriteThroughMockPreservesEnclosingStreamFilter(): void
+    {
+        CLI::write('before mock');
+        $this->assertStringContainsString('before mock', $this->getStreamFilterBuffer());
+
+        $io = new MockInputOutput();
+        CLI::setInputOutput($io);
+        CLI::write('through mock');
+        CLI::resetInputOutput();
+
+        // The mock captured its own write into its own buffer...
+        $this->assertStringContainsString('through mock', $io->getOutput());
+        // ...and left the enclosing StreamFilterTrait buffer untouched.
+        $this->assertStringNotContainsString('through mock', $this->getStreamFilterBuffer());
+
+        // The enclosing filter is still attached, so later writes are captured.
+        CLI::write('after mock');
+        $this->assertStringContainsString('before mock', $this->getStreamFilterBuffer());
+        $this->assertStringContainsString('after mock', $this->getStreamFilterBuffer());
+    }
+
+    public function testInputThroughMockPreservesEnclosingStreamFilter(): void
+    {
+        $io = new MockInputOutput();
+        $io->setInputs(['y']);
+        CLI::setInputOutput($io);
+        CLI::prompt('Continue?', ['y', 'n']);
+        CLI::resetInputOutput();
+
+        CLI::write('after prompt');
+        $this->assertStringContainsString('after prompt', $this->getStreamFilterBuffer());
+    }
+}

user_guide_src/source/changelogs/v4.7.4.rst

@@ -34,6 +34,7 @@ Bugs Fixed
 - **Database:** Fixed a bug where ``updateBatch()`` could be called after Query Builder ``where()`` conditions, even though it's not supported. In this situation, now the ``DatabaseException`` is thrown.
 - **HTTP:** Fixed a bug where the User Agent library reported Safari's WebKit version instead of the browser version from the ``Version`` token.
 - **Model:** Fixed a bug in ``Model::objectToRawArray()`` where the ``$recursive`` parameter was ignored.
+- **Testing:** Fixed a bug where using ``MockInputOutput`` within a test that also uses ``StreamFilterTrait`` tore down the trait's stream filters, so CLI output produced after the ``MockInputOutput`` interaction (such as in ``tearDown()``) was no longer captured and leaked to the console.
 
 See the repo's
 `CHANGELOG.md <https://github.com/codeigniter4/CodeIgniter4/blob/develop/CHANGELOG.md>`_