test: add typecheck

Author: vyudu

test/jumpsystem.jl

@@ -533,3 +533,21 @@ let
     Xsamp /= Nsims
     @test abs(Xsamp - Xf(0.2, p) < 0.05 * Xf(0.2, p))
 end
+
+@testset "JumpProcess simulation should be Int64 valued (#3446)" begin
+    @parameters p d
+    @variables X(t)
+    rate1   = p
+    rate2   = X*d
+    affect1 = [X ~ X + 1]
+    affect2 = [X ~ X - 1]
+    j1 = ConstantRateJump(rate1, affect1)
+    j2 = ConstantRateJump(rate2, affect2)
+
+    # Works.
+    @mtkbuild js = JumpSystem([j1, j2], t, [X], [p,d])
+    dprob = DiscreteProblem(js, [X => 15], (0.0, 10.), [p => 2.0, d => 0.5])
+    jprob = JumpProblem(js, dprob, Direct())
+    sol = solve(jprob, SSAStepper())
+    @test eltype(sol[X]) === Int64
+end