Stronger tests

Author: YingboMa

test/components.jl

@@ -19,6 +19,8 @@ function check_contract(sys)
 end
 
 function check_rc_sol(sol)
+    rpi = sol[rc_model.resistor.p.i]
+    @test any(!isequal(rpi[1]), rpi) # test that we don't have a constant system
     @test sol[rc_model.resistor.p.i] == sol[resistor.p.i] == sol[capacitor.p.i]
     @test sol[rc_model.resistor.n.i] == sol[resistor.n.i] == -sol[capacitor.p.i]
     @test sol[rc_model.capacitor.n.i] == sol[capacitor.n.i] == -sol[capacitor.p.i]
@@ -31,8 +33,9 @@ end
 include("../examples/rc_model.jl")
 
 @test ModelingToolkit.n_extra_equations(capacitor) == 2
-@test length(equations(structural_simplify(rc_model, allow_parameter = false))) > 1
+@test length(equations(structural_simplify(rc_model, allow_parameter = false))) == 2
 sys = structural_simplify(rc_model)
+@test length(equations(sys)) == 1
 check_contract(sys)
 @test !isempty(ModelingToolkit.defaults(sys))
 u0 = [capacitor.v => 0.0
@@ -141,6 +144,7 @@ sol = solve(prob, Tsit5())
 
 include("../examples/serial_inductor.jl")
 sys = structural_simplify(ll_model)
+@test length(equations(sys)) == 2
 check_contract(sys)
 u0 = states(sys) .=> 0
 @test_nowarn ODEProblem(sys, u0, (0, 10.0))