Move link!!/invlink!! tests back into DynamicPPL

test/varinfo.jl

@@ -387,6 +387,57 @@ DynamicPPL.getspace(::DynamicPPL.Sampler{MySAlg}) = (:s,)
         end
     end
 
+    @testset "link!! and invlink!!" begin
+        @model gdemo(x, y) = begin
+            s ~ InverseGamma(2, 3)
+            m ~ Uniform(0, 2)
+            x ~ Normal(m, sqrt(s))
+            y ~ Normal(m, sqrt(s))
+        end
+        model = gdemo(1.0, 2.0)
+
+        # Check that instantiating the model does not perform linking
+        vi = VarInfo()
+        meta = vi.metadata
+        model(vi, SampleFromUniform())
+        @test all(x -> !istrans(vi, x), meta.vns)
+
+        # Check that linking and invlinking set the `trans` flag accordingly
+        v = copy(meta.vals)
+        link!!(vi, model)
+        @test all(x -> istrans(vi, x), meta.vns)
+        invlink!!(vi, model)
+        @test all(x -> !istrans(vi, x), meta.vns)
+        @test meta.vals ≈ v atol = 1e-10
+
+        # Check that linking and invlinking preserves the values
+        vi = TypedVarInfo(vi)
+        meta = vi.metadata
+        @test all(x -> !istrans(vi, x), meta.s.vns)
+        @test all(x -> !istrans(vi, x), meta.m.vns)
+        v_s = copy(meta.s.vals)
+        v_m = copy(meta.m.vals)
+        link!!(vi, model)
+        @test all(x -> istrans(vi, x), meta.s.vns)
+        @test all(x -> istrans(vi, x), meta.m.vns)
+        invlink!!(vi, model)
+        @test all(x -> !istrans(vi, x), meta.s.vns)
+        @test all(x -> !istrans(vi, x), meta.m.vns)
+        @test meta.s.vals ≈ v_s atol = 1e-10
+        @test meta.m.vals ≈ v_m atol = 1e-10
+
+        # Transform only one variable (`s`) but not the others (`m`)
+        spl = DynamicPPL.Sampler(MySAlg(), model)
+        link!!(vi, spl, model)
+        @test all(x -> istrans(vi, x), meta.s.vns)
+        @test all(x -> !istrans(vi, x), meta.m.vns)
+        invlink!!(vi, spl, model)
+        @test all(x -> !istrans(vi, x), meta.s.vns)
+        @test all(x -> !istrans(vi, x), meta.m.vns)
+        @test meta.s.vals ≈ v_s atol = 1e-10
+        @test meta.m.vals ≈ v_m atol = 1e-10
+    end
+
     @testset "istrans" begin
         @model demo_constrained() = x ~ truncated(Normal(), 0, Inf)
         model = demo_constrained()