
A series of tests for examining unpolarised reflectivity calculation
correctness.

Each of the tests is described by a `test*` file in this directory. Those test
files have a series of header lines that can be used to describe the test, each
of the header lines is prefixed by #.
The next line is a string that refers to a file in the `layers` directory,
which specifies a slab-like model for which the reflectivity needs to be
calculated.
The next line is a string that refers to a file in the `data` directory
containing the validated values against which the reflectivity calculation is
to be checked. These 'datafiles' will eventually be standard ORSO format, but
for the time being they are Q (Å**-1), R, [dR (1sd) [, dQ (Å**-1) (1sd)]].

The layer specification file has the layout:

ignored     SLD_fronting ignored      ignored
thickness_1 SLD_1        iSLD_1       rough_fronting1
thickness_2 SLD_2        iSLD_2       rough_12
ignored     SLD_backing  iSLD_backing rough_backing2


The `ignored` values exist because the fronting and backing media have no
thickness. Absorption is also ignored in the fronting medium. The real and
imaginary parts of the SLD values have units (10**-6 Angstrom**-2).
