add tests

test/extensions/modelingtoolkit.jl

@@ -658,6 +658,43 @@ if GROUP == "All" || GROUP == "ModelingToolkitSIExt"
     end
 
     @testset "Exporting ModelingToolkit Model to SI Model" begin
-        # Add test of `mtk_to_si` function here, as well as identifiability functions when applied to its output.
+
+        # Creates MTK model and assesses its identifiability.
+        @parameters r1, r2, c1, c2, beta1, beta2, chi1, chi2
+        @variables t, x1(t), x2(t), y(t), u(t)
+        D= Differential(t)
+        eqs = [
+            D(x1) ~ r1 * x1 * (1 - c1 * x1) + beta1 * x1 * x2 / (chi1 + x2) + u,
+            D(x2) ~ r2 * x2 * (1 - c2 * x2) + beta2 * x1 * x2 / (chi2 + x1),
+        ]
+        measured_quantities = [y ~ x1]
+        ode_mtk = ODESystem(eqs, t, name = :mutualist)
+
+        global_id_1 = assess_identifiability(ode_mtk, measured_quantities = measured_quantities)
+        local_id_1 = assess_local_identifiability(ode_mtk, measured_quantities = measured_quantities)
+        ifs_1 = find_identifiable_functions(ode_mtk, measured_quantities = measured_quantities)
+
+        # Converts mtk model to si model, and assesses its identifiability.
+        si_model, _ = mtk_to_si(ode_mtk, measured_quantities)
+        global_id_2 = assess_identifiability(si_model)
+        local_id_2 = assess_local_identifiability(si_model)
+        ifs_2 = find_identifiable_functions(si_model)
+
+        # Converts the output dicts from StructuralIdentifiability functions from "weird symbol => stuff" to "symbol => stuff" (the output have some strange meta data which prevents equality checks, this enables this).
+        # Structural identifiability also provides variables like x (rather than x(t)). This is a bug, but we have to convert to make it work (now just remove any (t) to make them all equal).
+        function sym_dict(dict_in)
+            dict_out = Dict{Symbol,Any}()
+            for key in keys(dict_in)
+                sym_key = Symbol(key)
+                sym_key = Symbol(replace(String(sym_key), "(t)" => ""))
+                dict_out[sym_key] = dict_in[key]
+            end    
+            return dict_out
+        end
+
+        # Checks that the two approaches yields the same result
+        @test issetequal(sym_dict(local_id_1), sym_dict(local_id_2))
+        @test issetequal(sym_dict(local_id_1), sym_dict(local_id_2))
+        @test length(ifs_1) == length(ifs_2)   
     end
 end