Add test for the sparse Jacobian usage

test/DiffEqsWrappersTests/DiffEqsTests.jl

@@ -93,6 +93,14 @@ prob_iip = DAEProblem{true}(f_iip, u0, u0, tspan, differential_vars = [true,true
 # sol_iip = Sundials.solve(prob_iip, IDA(), reltol = 1e-8, abstol = 1e-8)
 # @show sol_iip.u
 
+# To explore the Sundials solver options, e.g., BE with fixed time step dtd
+f_iip = DAEFunction{true}(res!; jac = jac!, jac_prototype=J)
+# jac_prototype is the way to pass my pre-allocated jacobian matrix
+prob_iip = DAEProblem{true}(f_iip, u0, u0, tspan, differential_vars = trues(length(u0)))
+
+sol_iip = Sundials.solve(prob_iip, IDA(linear_solver=:KLU), reltol = 1e-8, abstol = 1e-8)
+#@show sol_iip.u
+
 # or iterator version
 # integ = init(prob_iip, IDA(), reltol = 1e-8, abstol = 1e-8)
 # step!(integ)