Test a system that should have a guess

Author: hersle

test/initializationsystem.jl

@@ -456,3 +456,11 @@ sys = structural_simplify(unsimp; fully_determined = false)
 sys = extend(sysx, sysy)
 @test length(equations(generate_initializesystem(sys))) == 2
 @test length(ModelingToolkit.guesses(sys)) == 1
+
+# https://github.com/SciML/ModelingToolkit.jl/issues/2873
+@testset "Error on missing defaults" begin
+    @variables x(t) y(t)
+    @named sys = ODESystem([x^2 + y^2 ~ 25, D(x) ~ 1], t)
+    ssys = structural_simplify(sys)
+    @test_throws ArgumentError ODEProblem(ssys, [x => 3], (0, 1), []) # y should have a guess
+end