In test compression / decompression schemes the objective is to achieve the highest compression without sacrificing fault coverage. In this paper, we propose a method to transform a test set in order to achieve higher compression without sacrificing fault coverage, while using statistical encoding techniques. The compression ratio of a test set depends on the entropy of the test set, and hence our test transformation method decreases the entropy of the test set without losing the fault coverage. Experimental results show that the proposed method transforms given test sets into highly compressible ones.