A device includes a test unit in a die. The test unit includes a physical test region including an active region, and a plurality of conductive lines over the active region and parallel to each other. The plurality of conductive lines has substantially a uniform spacing, wherein no contact plugs are directly over and connected to the plurality of conductive lines. The test unit further includes an electrical test region including a transistor having a gate formed of a same material, and at a same level, as the plurality of conductive lines; and contact plugs connected to a source, a drain, and the gate of the transistor. The test unit further includes an alignment mark adjacent the physical test region and the electrical test region.