Add a test for getstepsize()

test/mcmc/hmc.jl

@@ -329,6 +329,27 @@ using Turing
         @test pvalue(ApproximateTwoSampleKSTest(vec(results), vec(results_prior))) > 0.001
     end
 
+    @testset "getstepsize: Turing.jl#2400" begin
+        algs = [
+            HMC(0.1, 10),
+            HMCDA(0.8, 0.75),
+            NUTS(0.5),
+            NUTS(0, 0.5),
+        ]
+        @testset "$(alg)" for alg in algs
+            # Construct a HMC state by taking a single step
+            spl = Sampler(alg, gdemo_default)
+            hmc_state = DynamicPPL.initialstep(
+                Random.default_rng(),
+                gdemo_default,
+                spl,
+                DynamicPPL.VarInfo(gdemo_default)
+            )[2]
+            # Check that we can obtain the current step size
+            @test Turing.Inference.getstepsize(spl, hmc_state) isa Float64
+        end
+    end
+
     @testset "Check ADType" begin
         alg = HMC(0.1, 10; adtype=adbackend)
         m = DynamicPPL.contextualize(