🔨 Refactor test to use MTZ TSP

- This is a much harder model that is more likely to not be solved within the allowed time

pyomo/solvers/tests/checks/test_CPLEXDirect.py

@@ -8,10 +8,14 @@
 #  This software is distributed under the 3-clause BSD License.
 #  ___________________________________________________________________________
 
+import sys
+from itertools import product
+from random import random, seed
+
 import pyutilib.th as unittest
-from pyomo.opt import *
+
 from pyomo.environ import *
-import sys
+from pyomo.opt import *
 
 try:
     import cplex
@@ -116,25 +120,75 @@ def test_infeasible_mip(self):
     @unittest.skipIf(not cplexpy_available,
                      "The 'cplex' python bindings are not available")
     def test_no_solution_mip(self):
-        model = ConcreteModel()
-        model.S = RangeSet(0, 9)
-        model.P = list(range(10))
-        model.X = Var(model.S, within=Binary)
-        model.C1 = Constraint(expr=summation(model.X) == 1)
-        model.C2 = Constraint(expr=model.X[0] >= 2)
-        model.O = Objective(expr=sum_product(model.P, model.X), sense=minimize)
+        def build_mtz_tsp_model(nodes, links, distances):
+            # Taken from examples/pyomo/callbacks/tsp.py
+            model = ConcreteModel()
+
+            model.POINTS = Set(initialize=nodes, ordered=True)
+            model.POINTS_LESS_FIRST = Set(initialize=nodes[1:], ordered=True)
+            model.LINKS = Set(initialize=links, ordered=True)
+            model.LINKS_LESS_FIRST = Set(
+                initialize=[
+                    (i, j) for (i, j) in links if i in nodes[1:] and j in nodes[1:]
+                ],
+                ordered=True,
+            )
+
+            model.N = len(nodes)
+            model.d = Param(model.LINKS, initialize=distances)
+
+            model.Z = Var(model.LINKS, domain=Binary)
+            model.FLOW = Var(
+                model.POINTS_LESS_FIRST,
+                domain=NonNegativeReals,
+                bounds=(0, model.N - 1),
+            )
+
+            model.InDegrees = Constraint(
+                model.POINTS,
+                rule=lambda m, i: sum(
+                    model.Z[i, j] for (i_, j) in model.LINKS if i == i_
+                )
+                == 1,
+            )
+            model.OutDegrees = Constraint(
+                model.POINTS,
+                rule=lambda m, i: sum(
+                    model.Z[j, i] for (j, i_) in model.LINKS if i == i_
+                )
+                == 1,
+            )
+
+            model.FlowCon = Constraint(
+                model.LINKS_LESS_FIRST,
+                rule=lambda m, i, j: model.FLOW[i] - model.FLOW[j] + m.N * m.Z[i, j]
+                <= m.N - 1,
+            )
+
+            model.tour_length = Objective(
+                expr=sum_product(model.d, model.Z), sense=minimize
+            )
+            return model
 
         with SolverFactory("cplex", solver_io="python") as opt:
             # Set the `options` such that CPLEX cannot determine the problem as infeasible within the time allowed
-            opt.options['timelimit'] = 0
-            opt.options['preprocessing_presolve'] = 0
-            opt.options['simplex_limits_iterations'] = 1
-            opt.options['mip_limits_nodes'] = 1
+            opt.options["timelimit"] = 0.0001
+            opt.options["preprocessing_presolve"] = 0
+
+            nodes = list(range(15))
+            links = list((i, j) for i, j in product(nodes, nodes) if i != j)
+
+            seed(0)
+            distances = {link: random() for link in links}
+
+            model = build_mtz_tsp_model(nodes, links, distances)
 
             results = opt.solve(model)
 
-            self.assertEqual(results.solver.termination_condition,
-                             TerminationCondition.noSolution)
+            self.assertEqual(results.solver.status, SolverStatus.warning)
+            self.assertEqual(
+                results.solver.termination_condition, TerminationCondition.noSolution
+            )
 
     @unittest.skipIf(not cplexpy_available,
                      "The 'cplex' python bindings are not available")