test: fs: Add ext4l filesystem tests

Add initial tests for the ext4l filesystem driver:

- fs_test_ext4l_probe_norun: verifies the driver can probe and mount
  an ext4 filesystem
- fs_test_ext4l_msgs_norun: verifies the ext4l_msgs env var causes
  mount messages to be printed

The C tests use UTF_MANUAL flag and accept fs_image argument,
following the pattern established by fs_basic.c. The Python wrapper
creates an ext4 image and calls the C tests.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

test/py/tests/test_fs/test_ext4l.py

@@ -0,0 +1,59 @@
+# SPDX-License-Identifier: GPL-2.0+
+# Copyright 2025 Canonical Ltd
+# Written by Simon Glass <simon.glass@canonical.com>
+#
+# Test for ext4l filesystem driver
+
+"""
+Test ext4l filesystem probing via C unit test.
+"""
+
+import os
+from subprocess import CalledProcessError, check_call
+
+import pytest
+
+
+@pytest.mark.boardspec('sandbox')
+class TestExt4l:
+    """Test ext4l filesystem operations."""
+
+    @pytest.fixture(scope='class')
+    def ext4_image(self, u_boot_config):
+        """Create an ext4 filesystem image for testing.
+
+        Args:
+            u_boot_config (u_boot_config): U-Boot configuration.
+
+        Yields:
+            str: Path to the ext4 image file.
+        """
+        image_path = os.path.join(u_boot_config.persistent_data_dir,
+                                  'ext4l_test.img')
+        try:
+            # Create a 64MB ext4 image
+            check_call(f'dd if=/dev/zero of={image_path} bs=1M count=64 2>/dev/null',
+                       shell=True)
+            check_call(f'mkfs.ext4 -q {image_path}', shell=True)
+        except CalledProcessError:
+            pytest.skip('Failed to create ext4 image')
+
+        yield image_path
+
+        # Cleanup
+        if os.path.exists(image_path):
+            os.remove(image_path)
+
+    def test_probe(self, ubman, ext4_image):
+        """Test that ext4l can probe an ext4 filesystem."""
+        with ubman.log.section('Test ext4l probe'):
+            output = ubman.run_command(
+                f'ut -f fs fs_test_ext4l_probe_norun fs_image={ext4_image}')
+            assert 'failures: 0' in output
+
+    def test_msgs(self, ubman, ext4_image):
+        """Test that ext4l_msgs env var produces mount messages."""
+        with ubman.log.section('Test ext4l msgs'):
+            output = ubman.run_command(
+                f'ut -f fs fs_test_ext4l_msgs_norun fs_image={ext4_image}')
+            assert 'failures: 0' in output