diff --git a/test/io/test_postprocess.jl b/test/io/test_postprocess.jl
new file mode 100644
index 0000000..402ed39
--- /dev/null
+++ b/test/io/test_postprocess.jl
@@ -0,0 +1,23 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+using JuliaFEM, Test
+
+## interpolate from a set of elements
+
+element1 = Element(Seg2, (1, 2))
+element2 = Element(Seg2, (2, 3))
+X = Dict(1 => [0.0], 2 => [1.0], 3 => [2.0])
+T = Dict(1 => [0.0], 2 => [1.0], 3 => [0.0])
+problem = Problem(Heat, "foo", 1)
+add_elements!(problem, element1, element2)
+problem_elements = get_elements(problem)
+update!(problem_elements, "geometry", X)
+update!(problem_elements, "temperature", T)
+@test isnan(problem("temperature", [-0.1], 0.0))
+@test isapprox(problem("temperature", [0.0], 0.0), [0.0])
+@test isapprox(problem("temperature", [0.5], 0.0), [0.5])
+@test isapprox(problem("temperature", [1.0], 0.0), [1.0])
+@test isapprox(problem("temperature", [1.5], 0.0), [0.5])
+@test isapprox(problem("temperature", [2.0], 0.0), [0.0])
+@test isnan(problem("temperature", [ 2.1], 0.0))