.

go/zodb/storage/demo/demo.go

@@ -68,7 +68,7 @@ func (d *Storage) Sync(ctx context.Context) (head zodb.Tid, err error) {
 		}
 	}()
 
-	head, err := d.δ.Sync(ctx)
+	head, err = d.δ.Sync(ctx)
 	if err != nil {
 		return zodb.InvalidTid, err
 	}

go/zodb/storage/demo/demo_test.go

@@ -170,7 +170,25 @@ func TestWatch(t *testing.T) {
 }
 
 
-// TODO change base -> demo shutdown
+// TestBaseMutate verifies that demo detect if base mutates.
+func TestBaseMutate(t *testing.T) {
+	withDemo(t, func(t *testing.T, ddat *DemoData, ddrv *Storage) {
+		X := xtesting.FatalIf(t)
+
+		head, err := ddrv.Sync(context.Background())
+		if !(head == 0 && err == nil) {
+			t.Fatalf("sync0: head=%s  err=%s", head, err)
+		}
+
+		_, err = xtesting.ZPyCommitRaw(ddat.base, 0, xtesting.ZRawObject{
+			Oid:  1,
+			Data: []byte("ZZZ"),
+		});  X(err)
+
+		head, err = ddrv.Sync(context.Background())
+		// XXX verify err
+	})
+}
 
 func demoOpen(zurl string, opt *zodb.DriverOptions) (_ *Storage, at0 zodb.Tid, err error) {
 	defer xerr.Contextf(&err, "opendemo %s", zurl)