A test pad structure in a back-end-of-line metal interconnect structure is formed by repeated use of the same mask set, which includes a first line level mask, a first via level mask, a second line level mask, and a second via level mask. The test pad structure includes a two-dimensional array of test pads such that a first row is connected to a device macro structure in the same level, and test pads in another row are electrically connected to another device macro structure of the same design at an underlying level. The lateral shifting of electrical connection among pads located at different levels is enabled by lateral extension portions that protrude from pads and via structures that contact the lateral extension portions. This test pad structure includes more levels of testable metal interconnect structure than the number of used lithographic masks.