  The critical issue in cosmology today lies in determining if the cosmological
constant is the underlying ingredient of dark energy. Our profound lack of
understanding of the physics of dark energy places severe constrains on our
ability to say anything about its possible dynamical nature. Quoted errors on
the equation of state, w(z), are so heavily dependent on necessarily
over-simplified parameterisations they are at risk of being rendered
meaningless. Moreover, the existence of degeneracies between the reconstructed
w(z) and the matter and curvature densities weakens any conclusions still
further. We propose consistency tests for the cosmological constant which
provide a direct observational signal if Lambda is wrong, regardless of the
densities of matter and curvature. As an example of its utility, our flat case
test can warn of a small transition from w(z)=-1 of 20% from SNAP quality data
at 4-sigma, even when direct reconstruction techniques see virtually no
evidence for deviation from Lambda. It is shown to successfully rule out a wide
range of non-Lambda dark energy models with no reliance on knowledge of Omega_m
using SNAP-quality data and a large range for using 10^5 supernovae as
forecasted for LSST.
