Add tests

Author: YingboMa

test/components.jl

@@ -93,6 +93,12 @@ u0 = [
       resistor.v => 0.0
      ]
 prob = ODEProblem(sys, u0, (0, 10.0))
-sol = solve(prob, Rodas5())
+sol = solve(prob, Rodas4())
+
+@test sol[resistor.p.i] == sol[capacitor.p.i]
+@test sol[resistor.n.i] == -sol[capacitor.p.i]
+@test sol[capacitor.n.i] == -sol[capacitor.p.i]
+@test iszero(sol[ground.g.i])
+@test iszero(sol[ground.g.v])
 #using Plots
 #plot(sol)