made an draft test case, which is unfinished

core/test/validation_test.jl

@@ -401,3 +401,24 @@ end
     @test logger.logs[2].message ==
           "Basin / subgrid_level subgrid_id 1 has repeated element levels, this cannot be interpolated."
 end
+
+"""@testitem "negative demand"
+    using Ribasim
+    using Logging
+
+    toml_path = normpath(
+        @__DIR__,
+        "../../generated_testmodels/invalid_discrete_control/ribasim.toml"
+    )
+
+    @test ispath(toml_path)
+
+    logger = TestLogger()
+
+    with_logger(logger) do
+        @test_throws "Demand of user node $id with priority #$p_itp should be non-negative" Ribasim.User(
+            [Ribasim.NodeID(1)],
+            []
+        )
+    end
+end"""