InternalSolver: Better specify and test infeasibility

miplearn/solvers/tests/__init__.py

@@ -3,8 +3,11 @@
 #  Released under the modified BSD license. See COPYING.md for more details.
 
 from inspect import isclass
-from typing import List, Callable
+from typing import List, Callable, Any
 
+from pyomo import environ as pe
+
+from miplearn.instance import Instance, PyomoInstance
 from miplearn.problems.knapsack import KnapsackInstance, GurobiKnapsackInstance
 from miplearn.solvers.gurobi import GurobiSolver
 from miplearn.solvers.internal import InternalSolver
@@ -13,28 +16,55 @@ from miplearn.solvers.pyomo.gurobi import GurobiPyomoSolver
 from miplearn.solvers.pyomo.xpress import XpressPyomoSolver
 
 
-def _get_instance(solver):
-    def _is_subclass_or_instance(obj, parent_class):
-        return isinstance(obj, parent_class) or (
-            isclass(obj) and issubclass(obj, parent_class)
-        )
+class InfeasiblePyomoInstance(PyomoInstance):
+    def to_model(self) -> pe.ConcreteModel:
+        model = pe.ConcreteModel()
+        model.x = pe.Var(domain=pe.Binary)
+        model.OBJ = pe.Objective(expr=model.x, sense=pe.maximize)
+        model.eq = pe.Constraint(expr=model.x >= 2)
+        return model
 
+
+class InfeasibleGurobiInstance(Instance):
+    def to_model(self) -> Any:
+        import gurobipy as gp
+        from gurobipy import GRB
+
+        model = gp.Model()
+        x = model.addVars(1, vtype=GRB.BINARY, name="x")
+        model.addConstr(x[0] >= 2)
+        model.setObjective(x[0])
+        return model
+
+
+def _is_subclass_or_instance(obj, parent_class):
+    return isinstance(obj, parent_class) or (
+        isclass(obj) and issubclass(obj, parent_class)
+    )
+
+
+def _get_knapsack_instance(solver):
     if _is_subclass_or_instance(solver, BasePyomoSolver):
         return KnapsackInstance(
             weights=[23.0, 26.0, 20.0, 18.0],
             prices=[505.0, 352.0, 458.0, 220.0],
             capacity=67.0,
         )
-
     if _is_subclass_or_instance(solver, GurobiSolver):
         return GurobiKnapsackInstance(
             weights=[23.0, 26.0, 20.0, 18.0],
             prices=[505.0, 352.0, 458.0, 220.0],
             capacity=67.0,
         )
-
     assert False
 
 
+def _get_infeasible_instance(solver):
+    if _is_subclass_or_instance(solver, BasePyomoSolver):
+        return InfeasiblePyomoInstance()
+    if _is_subclass_or_instance(solver, GurobiSolver):
+        return InfeasibleGurobiInstance()
+
+
 def _get_internal_solvers() -> List[Callable[[], InternalSolver]]:
     return [GurobiPyomoSolver, GurobiSolver, XpressPyomoSolver]