test_model: add HiGHS solver conditionally

Author: rschwarz

test/test_model.py

@@ -4,6 +4,7 @@
 import pytest
 
 import mip
+import mip.highs
 from mip import (
     CBC,
     Column,
@@ -21,9 +22,11 @@
 )
 
 TOL = 1e-4
-SOLVERS = [CBC, HIGHS]
+SOLVERS = [CBC]
 if "GUROBI_HOME" in os.environ:
     SOLVERS += [GUROBI]
+if mip.highs.has_highs:
+    SOLVERS += [HIGHS]
 
 # Overall Optimization Tests