  We continue exploring the constraining capabilities of X-ray reflection
spectroscopy to test the Kerr-nature of astrophysical black holes and we
present the results of our analysis of two NuSTAR observations of Cygnus X-1 in
the soft state. We find that the final measurement can strongly depend on the
assumption of the intensity profile. We conclude that Cygnus X-1 is not
suitable for tests of general relativity using X-ray reflection spectroscopy
and we discuss the desired properties of a source to be a good candidate for
our studies.
