  We investigate expected constraints on the primordial tensor power spectrum
from the future cosmic microwave background polarization experiment LiteBIRD as
a test of multi-field inflation. We argue that the measurements of the
tensor-to-scalar ratio and the tensor spectral index, in combination with the
constraints on the scalar spectral index from the Planck observation, are
useful in testing multi-field inflation models. We also discuss implications
for multi-field inflationary model building.
