diff --git a/test/test_elements_add_fields.jl b/test/test_elements_add_fields.jl
new file mode 100644
index 0000000..e67c50e
--- /dev/null
+++ b/test/test_elements_add_fields.jl
@@ -0,0 +1,14 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+using JuliaFEM.Test
+
+using JuliaFEM.Core: Quad4, update!
+
+@testset "add new discrete constant time-variant field and interpolate it" begin
+    element = Quad4([1, 2, 3, 4])
+    element["my field"] = (0.0 => 0.0, 1.0 => 1.0)
+    @test isapprox(element("my field", [0.0, 0.0], 0.5), 0.5)
+    update!(element, "my field 2", 0.0 => 0.0, 1.0 => 1.0)
+    @test isapprox(element("my field 2", [0.0, 0.0], 0.5), 0.5)
+end
diff --git a/test/test_fields_time_interpolation.jl b/test/test_fields_time_interpolation.jl
new file mode 100644
index 0000000..bf8c303
--- /dev/null
+++ b/test/test_fields_time_interpolation.jl
@@ -0,0 +1,19 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/JuliaFEM.jl/blob/master/LICENSE.md
+
+using JuliaFEM.Test
+
+using JuliaFEM.Core: DCTV, DCTI
+
+@testset "test interpolation of discrete constant time-variant field" begin
+    f = DCTV(0.0 => 0.0, 1.0 => 1.0)
+    # time interpolation of time-variant fields results it's
+    # time-invariant counterpart
+    @test isapprox(f(-1.0), DCTI(0.0))
+    @test isapprox(f( 0.0), DCTI(0.0))
+    @test isapprox(f( 0.3), DCTI(0.3))
+    @test isapprox(f( 0.5), DCTI(0.5))
+    @test isapprox(f( 0.9), DCTI(0.9))
+    @test isapprox(f( 1.0), DCTI(1.0))
+    @test isapprox(f( 1.5), DCTI(1.0))
+end