Fix consistency check

Author: YingboMa

src/structural_transformation/utils.jl

@@ -76,7 +76,8 @@ function check_consistency(state::TearingState, ag = nothing)
 
     unassigned_var = []
     for (vj, eq) in enumerate(extended_var_eq_matching)
-        if eq === unassigned && (ag === nothing || !haskey(ag, vj))
+        if eq === unassigned && (ag === nothing || !haskey(ag, vj)) &&
+           !isempty(𝑑neighbors(graph, vj))
             push!(unassigned_var, fullvars[vj])
         end
     end

test/clock.jl

@@ -114,8 +114,7 @@ eqs = [yd ~ Sample(t, dt)(y)
 @named sys = ODESystem(eqs)
 ci, varmap = infer_clocks(sys)
 tss, inputs = ModelingToolkit.split_system(deepcopy(ci))
-sss, = ModelingToolkit.structural_simplify!(deepcopy(tss[2]), (inputs[2], ()),
-                                            check_consistency = false)
+sss, = ModelingToolkit.structural_simplify!(deepcopy(tss[2]), (inputs[2], ()))
 @test length(states(sss)) == 2
 z, z_t = states(sss)
 S = Shift(t, 1)