test: add tampered snapshot verification regression test

internal/verify/tampered_snapshot_test.go

@@ -0,0 +1,105 @@
+package verify
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	snaps "digiemu-core/pkg/snapshot"
+)
+
+func TestVerifyFailsForTamperedSnapshot(t *testing.T) {
+	root := repoRoot(t)
+
+	srcFixtureRoot := filepath.Join(root, "data", "test-fixtures")
+	tmpFixtureRoot := filepath.Join(t.TempDir(), "test-fixtures")
+
+	copyDir(t, srcFixtureRoot, tmpFixtureRoot)
+
+	snapshotPath := filepath.Join(tmpFixtureRoot, "snapshots", "demo", "snapshot.json")
+
+	raw, err := os.ReadFile(snapshotPath)
+	if err != nil {
+		t.Fatalf("read snapshot fixture: %v", err)
+	}
+
+	var snap map[string]any
+	if err := json.Unmarshal(raw, &snap); err != nil {
+		t.Fatalf("decode snapshot fixture: %v", err)
+	}
+
+	// Keep expected_hash_v1 unchanged, but tamper with deterministic snapshot scope.
+	snap["tampered_field"] = "this must change the reconstructed state hash"
+
+	tampered, err := json.MarshalIndent(snap, "", "  ")
+	if err != nil {
+		t.Fatalf("encode tampered snapshot fixture: %v", err)
+	}
+
+	if err := os.WriteFile(snapshotPath, tampered, 0o644); err != nil {
+		t.Fatalf("write tampered snapshot fixture: %v", err)
+	}
+
+	v := VerifierV1{
+		FixtureRoot: tmpFixtureRoot,
+		DataDir:     filepath.Join(root, "data"),
+		PreferData:  false,
+	}
+
+	result, err := v.Verify(snaps.Ref{Hash: "demo"})
+	if err != nil {
+		t.Fatalf("Verify returned unexpected error: %v", err)
+	}
+
+	if result.OK {
+		t.Fatalf("Verify must fail for a tampered snapshot; got OK=true message=%q", result.Message)
+	}
+
+	if !strings.Contains(result.Message, "hash mismatch") {
+		t.Fatalf("Verify should report hash mismatch for tampered snapshot; got message=%q errors=%v", result.Message, result.Errors)
+	}
+
+	if result.Expected == "" {
+		t.Fatal("Verify result should include expected hash")
+	}
+
+	if result.Got == "" {
+		t.Fatal("Verify result should include computed hash")
+	}
+
+	if result.Expected == result.Got {
+		t.Fatalf("tampered snapshot should produce different hash: expected=%s got=%s", result.Expected, result.Got)
+	}
+}
+
+func copyDir(t *testing.T, src, dst string) {
+	t.Helper()
+
+	if err := filepath.WalkDir(src, func(path string, d os.DirEntry, walkErr error) error {
+		if walkErr != nil {
+			return walkErr
+		}
+
+		rel, err := filepath.Rel(src, path)
+		if err != nil {
+			return err
+		}
+
+		target := filepath.Join(dst, rel)
+
+		if d.IsDir() {
+			return os.MkdirAll(target, 0o755)
+		}
+
+		data, err := os.ReadFile(path)
+		if err != nil {
+			return err
+		}
+
+		return os.WriteFile(target, data, 0o644)
+	}); err != nil {
+		t.Fatalf("copy fixture dir: %v", err)
+	}
+}