tests/converter: modify unpack testcase

This patch modifies the unpack testcase to keep consistent with the
new `nydus-image unpack` interface in nydus-image.

Signed-off-by: Yifan Zhao <[email protected]>

pkg/converter/tool/builder.go

@@ -305,7 +305,41 @@ func Unpack(option UnpackOption) error {
 	}
 
 	if option.BackendConfigPath != "" {
-		args = append(args, "--backend-config", option.BackendConfigPath)
+		configFile, err := os.Open(option.BackendConfigPath)
+		if err != nil {
+			return errors.Wrapf(err, "fail to open backend config file %s", option.BackendConfigPath)
+		}
+		defer configFile.Close()
+
+		configBytes, err := os.ReadFile(option.BackendConfigPath)
+		if err != nil {
+			return errors.Wrapf(err, "fail to read backend config file %s", option.BackendConfigPath)
+		}
+
+		var config map[string]interface{}
+		if err := json.Unmarshal(configBytes, &config); err != nil {
+			return errors.Wrapf(err, "fail to unmarshal backend config file %s", option.BackendConfigPath)
+		}
+
+		backendConfigType, ok := config["backend"].(map[string]interface{})["type"]
+		if !ok {
+			return errors.New("backend config file should contain a valid backend type")
+		}
+
+		backendConfig, ok := config["backend"].(map[string]interface{})[backendConfigType.(string)]
+		if !ok {
+			return errors.New("failed to get backend config with type " + backendConfigType.(string))
+		}
+
+		backendConfigBytes, err := json.Marshal(backendConfig)
+		if err != nil {
+			return errors.Wrapf(err, "fail to marshal backend config %v", backendConfig)
+		}
+
+		logrus.Errorf("Backend config: %s", backendConfigBytes)
+
+		args = append(args, "--backend-type", backendConfigType.(string))
+		args = append(args, "--backend-config", string(backendConfigBytes))
 	} else if option.BlobPath != "" {
 		args = append(args, "--blob", option.BlobPath)
 	}