test: py: load: check null_dev_desc_ok dispatch

Some pytest modules exercising the dispatch added by
  fs: dispatch null_dev_desc_ok filesystems before lookup

test_load_semihosting.py:
  "load semihosting - <addr> <file>" and the optional
  [bytes] [pos] variant. Runs on qemu_arm64 with
  CONFIG_SEMIHOSTING=y; reuses test_hostfs.py's host-staged
  fixture.

test_load_sandbox.py:
  "load sandbox - <addr> <file>" and the optional [bytes] [pos]
  variant. Runs on sandbox (boardspec('sandbox')); the sandbox
  fstype is registered with name="sandbox" and
    null_dev_desc_ok=true,
  so the same fs_lookup_null_dev_info() helper that
  routes semihosting also routes the "sandbox".

A "load ubifs - <addr> <file>" test is intentionally not provided.
UBIFS is built on UBI on MTD, which requires some additional works
that are not available with qemu/sandbox-ing.

Signed-off-by: Vincent Jardin <vjardin@free.fr>
Reviewed-by: Simon Glass <sjg@chromium.org>

test/py/tests/test_load_sandbox.py

@@ -0,0 +1,51 @@
+# SPDX-License-Identifier:      GPL-2.0+
+# Copyright 2026 Free Mobile - Vincent Jardin
+
+"""Regression test for `load sandbox - <addr> <file>`.
+
+Exercises the null_dev_desc_ok dispatch added in
+"fs: dispatch null_dev_desc_ok filesystems before block lookup".
+
+It is the counterpart of test_load_semihosting.py
+"""
+
+import os
+import pytest
+
+
+@pytest.fixture(scope='session')
+def sandbox_fixture(u_boot_config):
+    """Host-staged fixture file read by `load sandbox`."""
+    path = os.path.join(u_boot_config.persistent_data_dir,
+                        'sandbox-fstype.txt')
+    with open(path, 'w', encoding='utf-8') as f:
+        f.write('Das U-Boot\n')   # 11 bytes, same as test_hostfs.py / semihosting
+    yield path
+    os.remove(path)
+
+
+@pytest.mark.boardspec('sandbox')
+def test_sandbox_load(ubman, sandbox_fixture):
+    """Run `load sandbox - <addr> <file>` and check the bytes."""
+    response = ubman.run_command(
+        f'load sandbox - $loadaddr {sandbox_fixture}')
+
+    # Fixture is "Das U-Boot\n" (11 bytes).
+    assert '11 bytes read' in response
+
+    # crc32("Das U-Boot\n") -- identical to the semihosting / hostfs checks.
+    response = ubman.run_command('crc32 $loadaddr $filesize')
+    assert '==> 60cfccfc' in response
+
+
+@pytest.mark.boardspec('sandbox')
+def test_sandbox_load_offset(ubman, sandbox_fixture):
+    """Run the [bytes] [pos] variant through the same dispatch."""
+    response = ubman.run_command(
+        f'load sandbox - $loadaddr {sandbox_fixture} 4 6')
+    # bytes=4 pos=6 over "Das U-Boot\n" -> "Boot".
+    assert '4 bytes read' in response
+
+    # crc32("Boot")
+    response = ubman.run_command('crc32 $loadaddr $filesize')
+    assert '==> e6df01fa' in response

test/py/tests/test_semihosting/conftest.py

@@ -6,9 +6,9 @@
 import os
 import pytest
 
-@pytest.fixture(scope='session')
+@pytest.fixture(scope='function')
 def semihosting_data(u_boot_config):
-    """Set up a file system to be used in semihosting tests
+    """Set up a new file for each semihosting test
 
     Args:
         u_boot_config -- U-Boot configuration.

test/py/tests/test_semihosting/test_load_semihosting.py

@@ -0,0 +1,38 @@
+# SPDX-License-Identifier:      GPL-2.0+
+# Copyright 2026 Free Mobile - Vincent Jardin
+
+"""Regression test for `load semihosting - <addr> <file>`.
+
+Companion to test_hostfs.py: same fixture, same crc32, different
+fstype routing:
+see the doc/usage/cmd/load.rst "Null-block-device interfaces" section.
+"""
+
+import pytest
+
+
+@pytest.mark.buildconfigspec('semihosting')
+def test_semihosting_load(ubman, semihosting_data):
+    """Run `load semihosting - <addr> <file>` and check the bytes."""
+    response = ubman.run_command(
+        f'load semihosting - $loadaddr {semihosting_data}')
+
+    # Fixture is "Das U-Boot\n" (11 bytes).
+    assert '11 bytes read' in response
+
+    # crc32("Das U-Boot\n")
+    response = ubman.run_command('crc32 $loadaddr $filesize')
+    assert '==> 60cfccfc' in response
+
+
+@pytest.mark.buildconfigspec('semihosting')
+def test_semihosting_load_offset(ubman, semihosting_data):
+    """Run the [bytes] [pos] variant through the same dispatch."""
+    response = ubman.run_command(
+        f'load semihosting - $loadaddr {semihosting_data} 4 6')
+    # bytes=4 pos=6 over "Das U-Boot\n" -> "Boot".
+    assert '4 bytes read' in response
+
+    # crc32("Boot")
+    response = ubman.run_command('crc32 $loadaddr $filesize')
+    assert '==> e6df01fa' in response