Systems of struct class cannot be used with the "predict" command. Convert the system to an identified model first, such as by using the "idss" command.

Training Side
  model = fitcecoc(train_feature, train_label, 'Learners', 'Linear', 'Coding', 'onevsall', 'ObservationsIn', 'columns');

Tets side 
 predictedLabels = predict(model,test_feature);
 confMat = confusionmat(test_label, predictedLabels);
 confMat = bsxfun(@rdivide,confMat,sum(confMat,2))
 mean(diag(confMat))
 it is giving error at this line confMat = confusionmat(test_label, predictedLabels);