test: fit: add test case for invalid default configuration reference

Recent changes to mkimage introduced a validation step to ensure that
the 'default' property under the /configurations node in a FIT image
references a valid configuration subnode. If the referenced node is
missing, mkimage will now return an error.

This patch adds a Python test case to verify that mkimage correctly
fails when the 'default' configuration does not exist. The test creates
a minimal ITS with an invalid default reference and checks that mkimage
produces the expected error message.

Signed-off-by: Aristo Chen <aristo.chen@canonical.com>

1 files changed, 45 insertions, 0 deletions

diff --git a/test/py/tests/test_fit_mkimage_validate.py b/test/py/tests/test_fit_mkimage_validate.py
index af56f08ca10..ef974c8c762 100644
--- a/test/py/tests/test_fit_mkimage_validate.py
+++ b/test/py/tests/test_fit_mkimage_validate.py
@@ -7,6 +7,7 @@ import os
 import subprocess
 import pytest
 import fit_util
+import re
 
 @pytest.mark.boardspec('sandbox')
 @pytest.mark.requiredtool('dtc')
@@ -56,3 +57,47 @@ def test_fit_invalid_image_reference(ubman):
     assert result.returncode != 0, "mkimage should fail due to missing image reference"
     assert "references undefined image 'notexist'" in result.stderr
 
+def test_fit_invalid_default_config(ubman):
+    """Test that mkimage fails when default config is missing"""
+
+    its_fname = fit_util.make_fname(ubman, "invalid.its")
+    itb_fname = fit_util.make_fname(ubman, "invalid.itb")
+    kernel = fit_util.make_kernel(ubman, 'kernel.bin', 'kernel')
+
+    # Write ITS with an invalid reference to a nonexistent default config
+    its_text = '''
+/dts-v1/;
+
+/ {
+    images {
+        kernel@1 {
+            description = "Test Kernel";
+            data = /incbin/("kernel.bin");
+            type = "kernel";
+            arch = "sandbox";
+            os = "linux";
+            compression = "none";
+            load = <0x40000>;
+            entry = <0x40000>;
+        };
+    };
+
+    configurations {
+        default = "conf@1";
+        conf@2 {
+            kernel = "kernel@1";
+        };
+    };
+};
+'''
+
+    with open(its_fname, 'w') as f:
+        f.write(its_text)
+
+    mkimage = os.path.join(ubman.config.build_dir, 'tools/mkimage')
+    cmd = [mkimage, '-f', its_fname, itb_fname]
+
+    result = subprocess.run(cmd, capture_output=True, text=True)
+
+    assert result.returncode != 0, "mkimage should fail due to missing default config"
+    assert re.search(r"Default configuration '.*' not found under /configurations", result.stderr)