Fix Bridges.runtests when model has no variable (#2499)

src/Bridges/Bridges.jl

@@ -283,7 +283,10 @@ function runtests(
         Test.@test all(isnothing, MOI.get(model, attr, x))
         primal_start = fill(constraint_start, length(x))
         MOI.set(model, attr, x, primal_start)
-        Test.@test MOI.get(model, attr, x) ≈ primal_start
+        if !isempty(x)
+            # ≈ does not work if x is empty because the return of get is Any[]
+            Test.@test MOI.get(model, attr, x) ≈ primal_start
+        end
     end
     # Test ConstraintPrimalStart and ConstraintDualStart
     for (F, S) in MOI.get(model, MOI.ListOfConstraintTypesPresent())

test/Bridges/Constraint/flip_sign.jl

@@ -436,6 +436,19 @@ function test_runtests()
         VectorNonlinearFunction([-(2.1 * x - 1.0)]) in Nonnegatives(1)
         """,
     )
+    MOI.Bridges.runtests(
+        MOI.Bridges.Constraint.GreaterToLessBridge,
+        model -> MOI.add_constraint(
+            model,
+            zero(MOI.ScalarAffineFunction{Float64}),
+            MOI.GreaterThan(1.0),
+        ),
+        model -> MOI.add_constraint(
+            model,
+            zero(MOI.ScalarAffineFunction{Float64}),
+            MOI.LessThan(-1.0),
+        ),
+    )
     return
 end