test: add DynamicQuantities+Measurements downstream test

Adds `test/downstream/dynamicquantities_measurements.jl` covering a
Tsit5 solve of a problem whose state type combines DynamicQuantities
units with Measurements uncertainty propagation. Wires it into the
existing `Downstream` CI group so the extra deps (DynamicQuantities,
plus the existing Measurements) stay in `test/downstream/Project.toml`
and don't leak into `OrdinaryDiffEqCore`'s own test deps.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>

Author: MilesCranmerBot

test/downstream/Project.toml

@@ -1,6 +1,7 @@
 [deps]
 ADTypes = "47edcb42-4c32-4615-8424-f2b9edc5f35b"
 DifferentiationInterface = "a0c0ee7d-e4b9-4e03-894e-1c5f64a51d63"
+DynamicQuantities = "06fc5a27-2a28-4c7c-a15d-362465fb6821"
 Enzyme = "7da242da-08ed-463a-9acd-ee780be4f1d9"
 FiniteDiff = "6a86dc24-6348-571c-b903-95158fe2bd41"
 Measurements = "eff96d63-e80a-5855-80a2-b1b0885c5ab7"
@@ -11,6 +12,7 @@ StochasticDiffEq = "789caeaf-c7a9-5a7d-9973-96adeb23e2a0"
 [compat]
 ADTypes = "1.16"
 DifferentiationInterface = "0.6.54, 0.7"
+DynamicQuantities = "1.8"
 Enzyme = "0.13"
 FiniteDiff = "2.27"
 Measurements = "2.9"

test/downstream/dynamicquantities_measurements.jl

@@ -0,0 +1,21 @@
+using OrdinaryDiffEq
+using DynamicQuantities
+using Measurements
+using Test
+
+@testset "DynamicQuantities units + Measurements uncertainty" begin
+    u0 = (1.0 ± 0.1) * (1.0u"m")
+    tspan = (0.0u"s", 1.0u"s")
+
+    f(u, p, t) = u / (1u"s")
+    prob = ODEProblem(f, u0, tspan)
+
+    sol = solve(prob, Tsit5(); abstol = 1.0e-9, reltol = 1.0e-9)
+
+    @test sol.u[end] isa typeof(u0)
+    @test eltype(sol.u) == typeof(u0)
+
+    uend_m = ustrip(u"m", sol.u[end])
+    @test isapprox(Measurements.value(uend_m), exp(1); atol = 1.0e-6)
+    @test Measurements.uncertainty(uend_m) > 0
+end

test/runtests.jl

@@ -190,6 +190,7 @@ end
         activate_downstream_env()
         @time @safetestset "Measurements Tests" include("downstream/measurements.jl")
         @time @safetestset "Time derivative Tests" include("downstream/time_derivative_test.jl")
+        @time @safetestset "DynamicQuantities + Measurements Tests" include("downstream/dynamicquantities_measurements.jl")
     end
 
     # AD tests - Enzyme/Zygote only on Julia <= 1.11 (see https://github.com/EnzymeAD/Enzyme.jl/issues/2699)