test empty model solution and improve error msg

src/Algorithm/basic/solveipform.jl

@@ -132,10 +132,9 @@ function optimize_with_moi!(optimizer::MoiOptimizer, form::Formulation, result::
     sync_solver!(optimizer, form)
     nbvars = MOI.get(form.optimizer.inner, MOI.NumberOfVariables())
     if nbvars <= 0
-        @warn "No variable in the formulation. Coluna does not call the solver."
-    else
-        MOI.optimize!(getinner(optimizer))
+        @warn "No variable in the formulation."
     end
+    MOI.optimize!(getinner(optimizer))
     termination_status!(result, optimizer)
     return
 end

src/Algorithm/interface.jl

@@ -73,7 +73,7 @@ get_storages_usage(algo::AbstractAlgorithm, model::AbstractModel) = Tuple{Abstra
     Returns algorithm's output.    
 """
 function run!(algo::AbstractAlgorithm, env::Env, data::AbstractData, input::AbstractInput)::AbstractOutput
-    error("run! not defined for algorithm $(typeof(algo)), data $(typeof(data)), and input $(typeof(input)).")
+    error("Cannot apply run! for arguments $(typeof(algo)), $(typeof(data)), $(typeof(input)).")
 end
 
 """

test/issues_tests.jl

@@ -73,6 +73,42 @@ function decomposition_with_constant_in_objective()
     @test objective_value(model) ≈ 307.5 + 2
 end
 
+# Issue #424
+# - If you try to solve an empty model with Coluna using a SolveIpForm or SolveLpForm
+#   as top solver, the objective value will be 0.
+# - If you try to solve an empty model using TreeSearchAlgorithm, then Coluna will
+#   throw an error because since there is no decomposition, there is no reformulation
+#   and TreeSearchAlgorithm must be run on a reformulation.
+function solve_empty_model()
+    coluna = JuMP.optimizer_with_attributes(
+        Coluna.Optimizer,
+        "params" => CL.Params(solver = ClA.SolveIpForm()),
+        "default_optimizer" => GLPK.Optimizer
+    )
+    model = BlockModel(coluna)
+    optimize!(model)
+    @test JuMP.objective_value(model) == 0
+
+    coluna = JuMP.optimizer_with_attributes(
+        Coluna.Optimizer,
+        "params" => CL.Params(solver = ClA.SolveLpForm(update_ip_primal_solution = true)),
+        "default_optimizer" => GLPK.Optimizer
+    )
+    model = BlockModel(coluna)
+    optimize!(model)
+    @test JuMP.objective_value(model) == 0
+
+    coluna = optimizer_with_attributes(
+        Coluna.Optimizer,
+        "params" => Coluna.Params(
+            solver = Coluna.Algorithm.TreeSearchAlgorithm()
+        ),
+        "default_optimizer" => GLPK.Optimizer
+    )
+    model = BlockModel(coluna)
+    @test_throws ErrorException optimize!(model)
+end
+
 function test_issues_fixed()
     @testset "no_decomposition" begin
         solve_with_no_decomposition()
@@ -85,6 +121,10 @@ function test_issues_fixed()
     @testset "decomposition_with_constant_in_objective" begin
         decomposition_with_constant_in_objective()
     end
+
+    @testset "solve_empty_model" begin
+        solve_empty_model()
+    end
 end
 
 test_issues_fixed()

test/unit/unit_tests.jl

@@ -4,8 +4,6 @@ include("containers/solsandbounds.jl")
 include("MathProg/types.jl")
 include("MathProg/variables.jl")
 
-include("algorithms/algorithm.jl")
-
 include("counters.jl")
 include("variable.jl")
 include("constraint.jl")
@@ -24,10 +22,6 @@ function unit_tests()
         end
     end
 
-    @testset "algorithm.jl" begin
-        algorithm_unit_tests()
-    end
-
     @testset "counters.jl" begin
         counters_unit_tests()
     end