Add test for modifying constraint function. There is a broken test

and one commented out as MockOptimizer fails getting the constraint
function.

Author: odow

src/Test/UnitTests/modifications.jl

@@ -118,6 +118,50 @@ function solve_coef_scalaraffine_lessthan(model::MOI.ModelLike, config::TestConf
 end
 modificationtests["solve_coef_scalaraffine_lessthan"] = solve_coef_scalaraffine_lessthan
 
+"""
+    solve_func_scalaraffine_lessthan(model::MOI.ModelLike, config::TestConfig)
+
+Test setting the function in a ScalarAffineFunction-in-LessThan
+constraint. If `config.solve=true` confirm that it solves correctly, and if
+`config.duals=true`, check that the duals are computed correctly.
+"""
+function solve_func_scalaraffine_lessthan(model::MOI.ModelLike, config::TestConfig)
+    MOI.empty!(model)
+    MOIU.loadfromstring!(model,"""
+        variables: x
+        maxobjective: 1.0x
+    """)
+    x = MOI.get(model, MOI.VariableIndex, "x")
+    c = MOI.addconstraint!(model,
+            MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(1.0, x)], 0.0),
+            MOI.LessThan(1.0)
+        )
+    if config.solve
+        test_model_solution(model, config;
+            objective_value   = 1.0,
+            variable_primal   = [(x, 1.0)],
+            constraint_primal = [(c, 1.0)],
+            constraint_dual   = [(c, -1.0)]
+        )
+    end
+    @test MOI.canset(model, MOI.ConstraintFunction(), typeof(c))
+    MOI.set!(model, MOI.ConstraintFunction(), c,
+        MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(2.0, x)], 0.0)
+    )
+    @test MOI.canget(model, MOI.ConstraintFunction(), typeof(c))
+    foo = MOI.get(model, MOI.ConstraintFunction(), c)
+    @test_broken foo == MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(2.0, x)], 0.0)
+    if config.solve
+        test_model_solution(model, config;
+            objective_value   = 0.5,
+            variable_primal   = [(x, 0.5)],
+            # constraint_primal = [(c, 1.0)],
+            constraint_dual   = [(c, -0.5)]
+        )
+    end
+end
+modificationtests["solve_func_scalaraffine_lessthan"] = solve_func_scalaraffine_lessthan
+
 """
     solve_const_vectoraffine_nonpos(model::MOI.ModelLike, config::TestConfig)
 

test/Test/unit.jl

@@ -226,6 +226,21 @@ end
         )
         MOIT.solve_coef_scalaraffine_lessthan(mock, config)
     end
+    @testset "solve_func_scalaraffine_lessthan" begin
+        MOIU.set_mock_optimize!(mock,
+            (mock::MOIU.MockOptimizer) -> MOIU.mock_optimize!(mock,
+                MOI.Success, (MOI.FeasiblePoint, [1.0]),
+                MOI.FeasiblePoint,
+                    (MOI.ScalarAffineFunction{Float64}, MOI.LessThan{Float64}) => [-1.0]
+            ),
+            (mock::MOIU.MockOptimizer) -> MOIU.mock_optimize!(mock,
+                MOI.Success, (MOI.FeasiblePoint, [0.5]),
+                MOI.FeasiblePoint,
+                    (MOI.ScalarAffineFunction{Float64}, MOI.LessThan{Float64}) => [-0.5]
+            )
+        )
+        MOIT.solve_func_scalaraffine_lessthan(mock, config)
+    end
     @testset "solve_const_vectoraffine_nonpos" begin
         MOIU.set_mock_optimize!(mock,
             (mock::MOIU.MockOptimizer) -> MOIU.mock_optimize!(mock,