Fix set! ConstraintFunction for mock optimizer

Author: blegat

src/Test/UnitTests/modifications.jl

@@ -150,7 +150,7 @@ function solve_func_scalaraffine_lessthan(model::MOI.ModelLike, config::TestConf
     )
     @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)
+    @test foo ≈ MOI.ScalarAffineFunction([MOI.ScalarAffineTerm(2.0, x)], 0.0)
     if config.solve
         test_model_solution(model, config;
             objective_value   = 0.5,

src/Utilities/mockoptimizer.jl

@@ -216,7 +216,7 @@ end
 
 MOI.canset(mock::MockOptimizer, ::MOI.ConstraintFunction, ::Type{C}) where C <: CI = true
 function MOI.set!(mock::MockOptimizer, ::MOI.ConstraintFunction, c::CI{F,S}, func::F) where {F<:MOI.AbstractFunction, S<:MOI.AbstractSet}
-    MOI.set!(mock.inner_model, MOI.ConstraintFunction(), xor_index(c), func)
+    MOI.set!(mock.inner_model, MOI.ConstraintFunction(), xor_index(c), xor_variables(func))
 end
 
 function MOI.canmodify(mock::MockOptimizer, obj::MOI.ObjectiveFunction, change)