Change Xpress Error Test

[rafabench]

Closes #160

[codecov]

Codecov Report

Merging #161 (926a258) into master (9790646) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #161   +/-   ##
=======================================
  Coverage   55.55%   55.55%           
=======================================
  Files           9        9           
  Lines        4156     4156           
=======================================
  Hits         2309     2309           
  Misses       1847     1847           

Impacted Files	Coverage Δ
src/api.jl	24.46% <0.00%> (ø)
src/lib.jl	15.63% <0.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 9790646...926a258. Read the comment docs.