diff --git a/src/FEMBase.jl b/src/FEMBase.jl
index d45f8a9..2a9fcbc 100644
--- a/src/FEMBase.jl
+++ b/src/FEMBase.jl
@@ -36,5 +36,6 @@ export Poi1, Seg2, Seg3, Tri3, Tri6, Tri7, Quad4, Quad8, Quad9,
 export update!, add_elements!, add!, get_gdofs, group_by_element_type,
        get_unknown_field_name, get_unknown_field_dimension,
        get_integration_points, initialize!, assemble!
+export DCTI, DVTI, DCTV, DVTV, CCTI, CVTI, CCTV, CVTV
 
 end
diff --git a/src/assembly.jl b/src/assembly.jl
index 2220905..09072fd 100644
--- a/src/assembly.jl
+++ b/src/assembly.jl
@@ -44,6 +44,11 @@ function assemble!(problem::Problem, time=0.0; auto_initialize=true)
     return true
 end
 
+function assemble!{P}(assembly::Assembly, problem::Problem{P}, element::Element, time)
+    warn("One must define assemble! function for problem of type $P. Not doing anything.")
+    return nothing
+end
+
 function assemble!(assembly::Assembly, problem::Problem, elements::Vector{Element}, time)
     warn("assemble!() this is default assemble operation, decreased performance can be expected without preallocation of memory!")
     for element in elements
diff --git a/src/problems.jl b/src/problems.jl
index f53e31c..f2eae3a 100644
--- a/src/problems.jl
+++ b/src/problems.jl
@@ -395,6 +395,11 @@ function get_unknown_field_dimension(problem::Problem)
     return problem.dimension
 end
 
+function get_unknown_field_name{P<:AbstractProblem}(::Type{P})
+    warn("The name of unknown field (e.g. displacement, temperature, ...) of the problem type must be given by defining function `get_unknown_field_name`")
+    return "N/A"
+end
+
 """ Return the name of the unknown field of this problem. """
 function get_unknown_field_name{P}(problem::Problem{P})
     return get_unknown_field_name(P)
diff --git a/test/runtests.jl b/test/runtests.jl
index 0ba8309..01b219d 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -6,6 +6,9 @@ using TimerOutputs
 const to = TimerOutput()
 
 test_files = String[]
+push!(test_files, "test_add_elements.jl")
+push!(test_files, "test_common_failures.jl")
+push!(test_files, "test_elements.jl")
 
 @testset "FEMBase.jl" begin
     for fn in test_files
diff --git a/test/test_add_elements.jl b/test/test_add_elements.jl
new file mode 100644
index 0000000..0641c0d
--- /dev/null
+++ b/test/test_add_elements.jl
@@ -0,0 +1,16 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/FEMBase.jl/blob/master/LICENSE
+
+using FEMBase
+using Base.Test
+
+type Dummy <: FEMBase.FieldProblem
+end
+
+@testset "add elements to problem" begin
+    problem = Problem(Dummy, "test", 2)
+    element = Element(Quad4, [1, 2, 3, 4])
+    elements = [element]
+    add_elements!(problem, elements)
+    @test problem.elements[1] == element
+end
diff --git a/test/test_common_failures.jl b/test/test_common_failures.jl
new file mode 100644
index 0000000..0af229e
--- /dev/null
+++ b/test/test_common_failures.jl
@@ -0,0 +1,15 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/FEMBase.jl/blob/master/LICENSE
+
+using FEMBase
+using Base.Test
+
+type Dummy <: FieldProblem end
+
+@testset "no unknown field name or assemble!-function defined" begin
+    el = Element(Quad4, [1, 2, 3, 4])
+    pr = Problem(Dummy, "problem", 2)
+    add_elements!(pr, [el])
+    assemble!(pr)
+    @test true
+end
diff --git a/test/test_elements.jl b/test/test_elements.jl
new file mode 100644
index 0000000..6e241e1
--- /dev/null
+++ b/test/test_elements.jl
@@ -0,0 +1,75 @@
+# This file is a part of JuliaFEM.
+# License is MIT: see https://github.com/JuliaFEM/FEMBase.jl/blob/master/LICENSE
+
+using FEMBase
+using Base.Test
+
+using FEMBase: group_by_element_type
+
+@testset "add time dependent field to element" begin
+    el = Element(Seg2, [1, 2])
+    u1 = Vector{Float64}[[0.0, 0.0], [0.0, 0.0]]
+    u2 = Vector{Float64}[[1.0, 1.0], [1.0, 1.0]]
+    update!(el, "displacement", 0.0 => u1)
+    update!(el, "displacement", 1.0 => u2)
+    @test length(el["displacement"]) == 2
+    @test isapprox(el("displacement", [0.0], 0.0), [0.0, 0.0])
+    @test isapprox(el("displacement", [0.0], 0.5), [0.5, 0.5])
+    @test isapprox(el("displacement", [0.0], 1.0), [1.0, 1.0])
+    el2 = Element(Poi1, [1])
+    update!(el2, "force 1", 0.0 => 1.0)
+end
+
+@testset "add CVTV field to element" begin
+    el = Element(Seg2, [1, 2])
+    f(xi, time) = xi[1]*time
+    update!(el, "my field", f)
+    v = el("my field", [1.0], 2.0)
+    @test isapprox(v, 2.0)
+end
+
+@testset "add DCTI to element" begin
+    el = Element(Quad4, [1, 2, 3, 4])
+    update!(el, "displacement load", DCTI([4.0, 8.0]))
+    @test isa(el["displacement load"], DCTI)
+    @test !isa(el["displacement load"].data, DCTI)
+    update!(el, "displacement load 2", [4.0, 8.0])
+    @test isa(el["displacement load 2"], DCTI)
+    update!(el, "temperature", [1.0, 2.0, 3.0, 4.0])
+    @test isa(el["temperature"], DVTI)
+    @test isapprox(el("displacement load", [0.0, 0.0], 0.0), [4.0, 8.0])
+end
+
+@testset "interpolate DCTI from element" begin
+    el = Element(Seg2, [1, 2])
+    update!(el, "foobar", 1.0)
+    fb = el("foobar", [0.0], 0.0)
+    @test isa(fb, Float64)
+    @test isapprox(fb, 1.0)
+end
+
+@testset "add elements to elements" begin
+    el1 = Element(Seg2, [1, 2])
+    el2 = Element(Seg2, [3, 4])
+    update!(el1, "master elements", [el2])
+    lst = el1("master elements", 0.0)
+    @test isa(lst, Vector)
+end
+
+@testset "extend basis" begin
+    el = Element(Quad4, [1, 2, 3, 4])
+    expected = [
+        0.25 0.00 0.25 0.00 0.25 0.00 0.25 0.00
+        0.00 0.25 0.00 0.25 0.00 0.25 0.00 0.25]
+    @test isapprox(el([0.0, 0.0], 0.0, 2), expected)
+end
+
+@testset "group elements" begin
+    e1 = Element(Seg2, [1, 2])
+    e2 = Element(Quad4, [1, 2, 3, 4])
+    elements = [e1, e2]
+    r = group_by_element_type(elements)
+    @test length(r) == 2
+    @test first(r[Element{Seg2}]) == e1
+    @test first(r[Element{Quad4}]) == e2
+end