Recently, active research has been conducted on Korean grammatical error correction on machine translation (MT) and automatic noise generation. However, there is no gold-standard test set for objective and official comparative analysis. A significant limitation is measuring the ill-defined performance because the experimental error types in the train set are also included in the test set. Moreover, error types in the training set are also included in the test set. Additionally, the types of errors for qualitative analysis are defined differently with no explicit guidelines. This study proposes a gold-standard test set called the Korean Neural Grammatical Correction Test set (K-NCT) for Korean grammatical error correction using a new error type classification guideline. To ensure the factuality and reliability of the proposal, we conduct a quantitative analysis using a commercialization system and human evaluation. Experimental results demonstrate that the proposed grammatical error correction test set has a well-balanced, diverse, and precise guideline. Our dataset is available at https://github.com/seonminkoo/K-NCT