An example cartridge includes a base having a channel configured to receive fluid, where the fluid includes a test sample to be tested on the cartridge, and a structure including at least part of a fluidic duct. The structure is configured to move relative to the base between a first position and a second position. In the first position, the channel and fluidic duct are aligned to create a fluidic connection between the channel and the fluidic duct and, in the second position, the channel and the fluidic duct are unaligned to block a fluidic connection between the channel and the fluidic duct.