A display panel and a testing method thereof, a display device are provided. The display panel includes a plurality of data lines and a plurality of test signal lines, an even number of adjacent data lines are grouped as a data line group, one test signal line is provided at a middle position of the data line group, a plurality of data line groups are in one-to-one correspondence with the plurality of test signal lines, each of the plurality of test signal lines includes a first extending part and a plurality of second extending parts coupled to the first extending part, and each of the second extending parts extends symmetrically at both sides of the first extending part.