diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index e978604..1dcf282 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -34,7 +34,7 @@ jobs:
           - os: windows-latest
             arch: x86
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}
@@ -59,7 +59,7 @@ jobs:
     name: Documentation
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - uses: julia-actions/setup-julia@v1
         with:
           version: "1"
diff --git a/Project.toml b/Project.toml
index fc831cc..53906f2 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,19 +1,23 @@
 name = "ConstraintDomains"
 uuid = "5800fd60-8556-4464-8d61-84ebf7a0bedb"
 authors = ["Jean-François Baffier"]
-version = "0.3.5"
+version = "0.3.6"
 
 [deps]
 ConstraintCommons = "e37357d9-0691-492f-a822-e5ea6a920954"
 Dictionaries = "85a47980-9c8c-11e8-2b9f-f7ca1fa99fb4"
 Intervals = "d8418881-c3e1-53bb-8760-2df7ec849ed5"
 PatternFolds = "c18a7f1d-76ad-4ce4-950d-5419b888513b"
+TestItemRunner = "f8b46487-2199-4994-9208-9a1283c18c0a"
+TestItems = "1c621080-faea-4a02-84b6-bbd5e436b8fe"
 
 [compat]
 ConstraintCommons = "0.1"
 Dictionaries = "0.3"
 Intervals = "1"
 PatternFolds = "0.2"
+TestItemRunner = "0.2"
+TestItems = "0.1"
 julia = "1.6"
 
 [extras]
diff --git a/src/ConstraintDomains.jl b/src/ConstraintDomains.jl
index 2051fc2..a230b68 100644
--- a/src/ConstraintDomains.jl
+++ b/src/ConstraintDomains.jl
@@ -4,6 +4,8 @@ module ConstraintDomains
 using ConstraintCommons
 using Dictionaries
 using PatternFolds
+using TestItemRunner
+using TestItems
 
 # Exports
 export AbstractDomain
diff --git a/src/common.jl b/src/common.jl
index f9c33a4..74a817a 100644
--- a/src/common.jl
+++ b/src/common.jl
@@ -55,7 +55,8 @@ get_domain(d::D) where {D<:AbstractDomain} = d.domain
 
 """
     to_domains(args...)
-TODO - doc
+
+Convert various arguments into valid domains format.
 """
 to_domains(domain_sizes::Vector{Int}) = map(ds -> domain(0:ds), domain_sizes)
 
@@ -66,6 +67,11 @@ end
 
 to_domains(X, ::Nothing) = to_domains(X)
 
+"""
+    Base.rand(d::Union{Vector{D},Set{D}, D}) where {D<:AbstractDomain}
+
+Extends `Base.rand` to (a collection of) domains.
+"""
 Base.rand(d::AbstractDomain) = rand(get_domain(d))
 
 Base.rand(d::Union{Vector{D},Set{D}}) where {D<:AbstractDomain} = map(rand, d)
@@ -73,3 +79,11 @@ Base.rand(d::Union{Vector{D},Set{D}}) where {D<:AbstractDomain} = map(rand, d)
 function Base.rand(d::V) where {D<:AbstractDomain,U<:Union{Vector{D},Set{D}},V<:AbstractVector{U}}
     return map(rand, d)
 end
+
+## SECTION - Test Items
+@testitem "EmptyDomain" tags = [:domains, :empty] begin
+    ed = domain()
+    @test domain_size(ed) == 0 == length(ed)
+    @test isempty(ed)
+    @test π ∉ ed
+end
diff --git a/src/continuous.jl b/src/continuous.jl
index dbd7407..6d7f5d2 100644
--- a/src/continuous.jl
+++ b/src/continuous.jl
@@ -72,9 +72,15 @@ function domain_size(itv::Intervals)
     return maximum(last, get_domain(itv)) - minimum(first, get_domain(itv))
 end
 
+# TODO - implement
 function merge_domains(d1::D, d2::D) where {D<:ContinuousDomain}
 end
 
+"""
+    intersect_domains(d₁, d₂)
+
+Compute the intersections of two domains.
+"""
 function intersect_domains(i₁::I1, i₂::I2) where {I1<:Interval,I2<:Interval}
     if i₁.first > i₂.first
         return intersect_domains(i₂, i₁)
@@ -102,4 +108,36 @@ function intersect_domains(d₁::D, d₂::D) where {T<:Real,D<:ContinuousDomain{
     return Intervals(new_itvls)
 end
 
+
+"""
+    Base.size(i::I) where {I <: Interval}
+
+Defines the size of an interval as its `span`.
+"""
 size(i::I) where {I <: Interval} = span(i)
+
+## SECTION - Test Items
+@testitem "ContinuousDomain" tags = [:domains, :continuous] default_imports=false begin
+    using ConstraintDomains, Intervals, Test
+    # import Base:size
+
+    d1 = domain(1.0..3.15)
+    d2 = domain(Interval{Open, Open}(-42.42, 5.0))
+
+    domains = [
+        d1,
+        d2,
+    ]
+
+    for d in domains
+        for x in [1, 2.3, π]
+            @test x ∈ d
+        end
+        for x in [5.1, π^π, Inf]
+            @test x ∉ d
+        end
+        @test rand(d) ∈ d
+        @test rand(d, 1) ∈ d
+        @test domain_size(d) > 0.0
+    end
+end
diff --git a/src/discrete.jl b/src/discrete.jl
index 87f9253..4770e73 100644
--- a/src/discrete.jl
+++ b/src/discrete.jl
@@ -73,6 +73,12 @@ Delete `value` from the list of points in `d`.
 """
 Base.delete!(d::SetDomain, value) = pop!(get_domain(d), value)
 
+
+"""
+    merge_domains(d₁::AbstractDomain, d₂::AbstractDomain)
+
+Merge two domains of same nature (discrete/contiuous).
+"""
 function merge_domains(rd₁::RangeDomain, rd₂::RangeDomain)
     d₁ = get_domain(rd₁)
     d₂ = get_domain(rd₂)
@@ -99,3 +105,52 @@ function to_domains(X, d::D) where {D <: DiscreteDomain}
     n::Int = length(first(X)) / domain_size(d)
     return fill(d, n)
 end
+
+## SECTION - Test Items
+@testitem "DiscreteDomain" tags = [:domain, :discrete, :set] begin
+    d1 = domain([4,3,2,1])
+    d2 = domain(1)
+    foreach(i -> add!(d2, i), 2:4)
+    domains = [
+        d1,
+        d2,
+    ]
+
+    for d in domains
+    # constructors and ∈
+        for x in [1,2,3,4]
+            @test x ∈ d
+        end
+    # length
+        @test length(d) == 4
+    # draw and ∈
+        @test rand(d) ∈ d
+    # add!
+        add!(d, 5)
+        @test 5 ∈ d
+    # delete!
+        delete!(d, 5)
+        @test 5 ∉ d
+        @test domain_size(d) == 3
+    end
+end
+
+@testitem "RangeDomain" tags = [:domain, :discrete, :range] begin
+    d1 = domain(1:5)
+    d2 = domain(1:.5:5)
+    domains = [
+        d1,
+        d2,
+    ]
+
+    for d in domains
+        for x in [1, 2, 3, 4, 5]
+            @test x ∈ d
+        end
+        for x in [42]
+            @test x ∉ d
+        end
+        @test rand(d) ∈ d
+    end
+
+end
diff --git a/src/explore.jl b/src/explore.jl
index cd60ce7..3d86781 100644
--- a/src/explore.jl
+++ b/src/explore.jl
@@ -5,6 +5,17 @@ struct ExploreSettings
     solutions_limit::Int
 end
 
+"""
+    ExploreSettings(
+        domains;
+        complete_search_limit = 10^6,
+        max_samplings = sum(domain_size, domains),
+        search = :flexible,
+        solutions_limit = floor(Int, sqrt(max_samplings)),
+    )
+
+Settings for the exploration of a search space composed by a collection of domains.
+"""
 function ExploreSettings(
     domains;
     complete_search_limit = 10^6,
@@ -15,6 +26,11 @@ function ExploreSettings(
     return ExploreSettings(complete_search_limit, max_samplings, search, solutions_limit)
 end
 
+"""
+    _explore(args...)
+
+Internals of the `explore` function. Behavior is automatically adjusted on the kind of exploration: `:flexible`, `:complete`, `:partial`.
+"""
 function _explore(domains, f, s, ::Val{:partial})
     solutions = Set{Vector{Int}}()
     non_sltns = Set{Vector{Int}}()
@@ -69,3 +85,11 @@ function explore(
     f = x -> concept(x; parameters...)
     return _explore(domains, f, settings, Val(settings.search))
 end
+
+## SECTION - Test Items
+@testitem "Exploration" tags = [:exploration] begin
+    domains = [domain([1,2,3,4]) for i in 1:4]
+    X, X̅ = explore(domains, allunique)
+    @test length(X) == factorial(4)
+    @test length(X̅) == 4^4 - factorial(4)
+end
diff --git a/src/general.jl b/src/general.jl
index 60798d6..40c7b53 100644
--- a/src/general.jl
+++ b/src/general.jl
@@ -1,5 +1,16 @@
+"""
+    Base.eltype(::AbstractDomain)
+
+Extend `eltype` for domains.
+"""
 Base.eltype(::D) where {T, D <: Union{DiscreteDomain{T}, ContinuousDomain{T}}} = T
 
+
+"""
+    Base.convert(::Type{Union{Intervals, RangeDomain}}, d::Union{Intervals, RangeDomain})
+
+Extends `Base.convert` for domains.
+"""
 function Base.convert(::Type{Intervals}, d::RangeDomain{T}) where {T <: Real}
     a, b = extrema(get_domain(d))
     return domain(Float64(a)..Float64(b))
diff --git a/test/runtests.jl b/test/runtests.jl
index 03ef0cf..b9e874d 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,83 +1,3 @@
-using ConstraintCommons
-using ConstraintDomains
-using Dictionaries
-using Intervals
-using Test
+using TestItemRunner
 
-@testset "ConstraintDomains.jl" begin
-    @testset "EmptyDomain" begin
-        ed = domain()
-        @test domain_size(ed) == 0 == length(ed)
-        @test isempty(ed)
-        @test π ∉ ed
-    end
-
-    @testset "DiscreteDomain" begin
-        d1 = domain([4,3,2,1])
-        d2 = domain(1)
-        foreach(i -> add!(d2, i), 2:4)
-        domains = Dictionary(1:2, [d1, d2])
-
-        for d in domains
-        # constructors and ∈
-            for x in [1,2,3,4]
-                @test x ∈ d
-            end
-        # length
-            @test length(d) == 4
-        # draw and ∈
-            @test rand(d) ∈ d
-        # add!
-            add!(d, 5)
-            @test 5 ∈ d
-        # delete!
-            delete!(d, 5)
-            @test 5 ∉ d
-            @test domain_size(d) == 3
-        end
-    end
-
-    @testset "ContinuousDomain" begin
-        d1 = domain(1.0..3.15)
-        d2 = domain(Interval{Open, Open}(-42.42, 5.0))
-        # d3 = domain([d1, d2])
-        domains = Dictionary(1:2, [d1, d2])
-
-        for d in domains
-            for x in [1, 2.3, π]
-                @test x ∈ d
-            end
-            for x in [5.1, π^π, Inf]
-                @test x ∉ d
-            end
-            @test rand(d) ∈ d
-            @test rand(d, 1) ∈ d
-            @test domain_size(d) > 0.0
-        end
-
-    end
-
-    @testset "RangeDomain" begin
-        d1 = domain(1:5)
-        d2 = domain(1:.5:5)
-        domains = Dictionary(1:2, [d1, d2])
-
-        for d in domains
-            for x in [1, 2, 3, 4, 5]
-                @test x ∈ d
-            end
-            for x in [42]
-                @test x ∉ d
-            end
-            @test rand(d) ∈ d
-        end
-
-    end
-
-    @testset "Exploration" begin
-        domains = [domain([1,2,3,4]) for i in 1:4]
-        X, X̅ = explore(domains, allunique)
-        @test length(X) == factorial(4)
-        @test length(X̅) == 4^4 - factorial(4)
-    end
-end
+@run_package_tests