  Solutions to the electroweak hierarchy problem typically introduce a new
symmetry to stabilize the quadratic ultraviolet sensitivity in the self-energy
of the Higgs boson. The new symmetry is either broken softly or collectively,
as for example in supersymmetric and little Higgs theories. At low energies
such theories contain naturalness partners of the Standard Model fields which
are responsible for canceling the quadratic divergence in the squared Higgs
mass. Post the discovery of any partner-like particles, we propose to test the
aforementioned cancellation by measuring relevant Higgs couplings. Using the
fermionic top partners in little Higgs theories as an illustration, we
construct a simplified model for naturalness and initiate a study on testing
naturalness. After electroweak symmetry breaking, naturalness in the top sector
requires $a_T = - \lambda_t^2$ at leading order, where $\lambda_t$ and $a_T$
are the Higgs couplings to a pair of top quarks and top partners, respectively.
Using a multivariate method of Boosted Decision Tree to tag boosted particles
in the Standard Model, we show that, with a luminosity of 30 $ab^{-1}$ at a 100
TeV $pp$-collider, naturalness could be tested with a precision of 10 % for a
top partner mass up to 2.5 TeV.
