The aim of this experiment is to follow the evolution of double twins in a magnesium alloy during in situ compression tests using scanning 3D X-ray diffraction with a small point-focus beam. While the growth of tension twins in magnesium alloys has successfully been mapped in 3D in the past, the nucleation and growth of compression and double twins have not been studied as deeply. We thus propose to perform micropillar compression tests in a nano-indenter set up on samples containing i) pristine grains, ii) grains with compression twins and iii) grains with double twins, to follow the growth of compression and double twins respectively. Using a 100-nm point-focus beam, we will measure the full strain tensor at sub-grain level at various applied loads and stages of twin growth, thus shedding light on the accommodation of deformation in magnesium alloys via complex twinning mechanisms.