test: add image download/checksum tests

tests/test_image.py

@@ -0,0 +1,30 @@
+import hashlib
+from pathlib import Path
+
+from metis.pkg import image
+
+
+def test_download_file_url(tmp_path):
+    src = tmp_path / "src.bin"
+    src.write_bytes(b"hello")
+    dest = tmp_path / "dest.bin"
+    image.Download(f"file://{src}", dest)
+    assert dest.read_bytes() == b"hello"
+
+
+def test_checksum_ok(tmp_path):
+    f = tmp_path / "file.bin"
+    f.write_bytes(b"abc")
+    checksum = "sha256:" + hashlib.sha256(b"abc").hexdigest()
+    image.VerifyChecksum(f, checksum)
+
+
+def test_checksum_bad(tmp_path):
+    f = tmp_path / "file.bin"
+    f.write_bytes(b"abc")
+    checksum = "sha256:deadbeef"
+    try:
+        image.VerifyChecksum(f, checksum)
+    except Exception:
+        return
+    raise AssertionError("expected checksum failure")