try test without relaxation

test/regression/test_regression.jl

@@ -0,0 +1,37 @@
+using OrdinaryDiffEq, DiffEqDevTools,  Test
+
+import ODEProblemLibrary: prob_ode_linear,
+                          prob_ode_2Dlinear
+
+
+probnum = prob_ode_linear
+prob = prob_ode_2Dlinear
+
+dts = (1 / 2) .^ (7:-1:4)
+testTol = 0.2
+
+### Tsit5()
+
+println("Tsit5")
+dts = (1 / 2) .^ (7:-1:3)
+sim = test_convergence(dts, probnum, Tsit5())
+@test abs.(sim.𝒪est[:l2] - 5) < testTol + 0.2
+sim = test_convergence(dts, prob, Tsit5())
+@test abs.(sim.𝒪est[:l2] - 5) < testTol + 0.2
+
+### Tsit5() with new structure
+
+println("Tsit5 with relaxation")
+dts = (1 / 2) .^ (7:-1:3)
+sim = test_convergence(dts, probnum, Tsit5_for_relaxation())
+@test abs.(sim.𝒪est[:l2] - 5) < testTol + 0.2
+#sim = test_convergence(dts, prob, Tsit5_for_relaxation())  # need to implement perform_step for not constant cache
+#@test abs.(sim.𝒪est[:l2] - 5) < testTol + 0.2              # need to implement perform_step for not constant cache
+
+
+sol1 = solve(probnum, Tsit5())
+sol2 = solve(probnum, Tsit5_for_relaxation())
+
+using Plots
+plot(sol1, label = "Old")
+plot!(sol2, label = "New")