modify ID to ChainID to avoid confusing

Signed-off-by: lixiaobing10051267 <li.xiaobing1@zte.com.cn>

layer/empty_test.go

@@ -9,7 +9,7 @@ import (
 
 func TestEmptyLayer(t *testing.T) {
 	if EmptyLayer.ChainID() != ChainID(DigestSHA256EmptyTar) {
-		t.Fatal("wrong ID for empty layer")
+		t.Fatal("wrong ChainID for empty layer")
 	}
 
 	if EmptyLayer.DiffID() != DigestSHA256EmptyTar {

layer/layer_test.go

@@ -231,7 +231,7 @@ func cacheID(l Layer) string {
 
 func assertLayerEqual(t *testing.T, l1, l2 Layer) {
 	if l1.ChainID() != l2.ChainID() {
-		t.Fatalf("Mismatched ID: %s vs %s", l1.ChainID(), l2.ChainID())
+		t.Fatalf("Mismatched ChainID: %s vs %s", l1.ChainID(), l2.ChainID())
 	}
 	if l1.DiffID() != l2.DiffID() {
 		t.Fatalf("Mismatched DiffID: %s vs %s", l1.DiffID(), l2.DiffID())