should be enough to build the kernelmode tests, under the rostests/modules subdirectory.
However, I cannot do this as Ninja seems to know nothing about a Kmtests target.
You need to run it from the top-level build output directory (or the reactos/ subdirectory when using RosBE-Unix) like all other build commands.
Also make sure that you enabled rostests when configuring -- configure.cmd -DENABLE_ROSTESTS=1