Abstract: To counteract condense dew on a transparent cover film (3) covering each well (2) in an array of wells which forms a test plate (1) having a lower side formed by the bottoms of the wells (2) and an upper side formed by the upper edges of the wells (2) onto which edges the cover film (3) is sealingly attached, the test plate (1) is for a set time placed with its lower surface contacting a cooling plate (5), which is by a cooling element (8) kept at a set temperature below the room temperature, and with its upper surface in a distance from a heating plate (4) which is by a heating element (7) kept at a set temperature higher than the room temperature.