test(cmakev2): Assert ELF output in Linux target build test

Made-with: Cursor

tools/test_build_system/buildv2/test_linux_build.py

@@ -2,6 +2,7 @@
 # SPDX-License-Identifier: Apache-2.0
 import logging
 import sys
+from pathlib import Path
 
 import pytest
 from test_build_system_helpers import IdfPyFunc
@@ -12,3 +13,6 @@ from test_build_system_helpers import IdfPyFunc
 def test_linux_target_build(idf_py: IdfPyFunc) -> None:
     logging.info('Can build for Linux target')
     idf_py('--preview', '-DIDF_TARGET=linux', 'build')
+    elf = Path('build/build_test_app.elf')
+    assert elf.exists(), 'ELF file was not produced by the Linux build'
+    assert elf.stat().st_size > 0, 'ELF file is empty — link step may have failed silently'