  We investigate the accuracy of weak lensing simulations by comparing the
results of five independently developed lensing simulation codes run on the
same input $N$-body simulation. Our comparison focuses on the lensing
convergence maps produced by the codes, and in particular on the corresponding
PDFs, power spectra and peak counts. We find that the convergence power spectra
of the lensing codes agree to $\lesssim 2\%$ out to scales $\ell \approx 4000$.
For lensing peak counts, the agreement is better than $5\%$ for peaks with
signal-to-noise $\lesssim 6$. We also discuss the systematic errors due to the
Born approximation, line-of-sight discretization, particle noise and smoothing.
The lensing codes tested deal in markedly different ways with these effects,
but they nonetheless display a satisfactory level of agreement. Our results
thus suggest that systematic errors due to the operation of existing lensing
codes should be small. Moreover their impact on the convergence power spectra
for a lensing simulation can be predicted given its numerical details, which
may then serve as a validation test.
