diff --git a/src/library/solution/abstract.jl b/src/library/solution/abstract.jl
index 282426e..402c927 100644
--- a/src/library/solution/abstract.jl
+++ b/src/library/solution/abstract.jl
@@ -25,10 +25,6 @@ function Base.isapprox(x::S, y::S; kws...) where {T,U,S<:AbstractSample{T,U}}
            state(x) == state(y)
 end
 
-Base.firstindex(::AbstractSolution)            = 1
-Base.firstindex(::AbstractSolution, ::Integer) = 1
-Base.lastindex(sol::AbstractSolution)          = length(sol)
-
 function hassample(sol::AbstractSolution, i::Integer)
     return 1 <= i <= length(sol)
 end
@@ -41,6 +37,10 @@ function sample(sol::AbstractSolution, i::Integer)
     end
 end
 
+Base.firstindex(::AbstractSolution)            = 1
+Base.firstindex(::AbstractSolution, ::Integer) = 1
+Base.lastindex(sol::AbstractSolution)          = length(sol)
+
 function Base.lastindex(sol::AbstractSolution, axis::Integer)
     if axis == 1
         return length(sol)
diff --git a/test/unit/library/solution.jl b/test/unit/library/solution.jl
index 48dbc05..4e6f336 100644
--- a/test/unit/library/solution.jl
+++ b/test/unit/library/solution.jl
@@ -160,7 +160,11 @@ function test_solution_sampleset()
 
         # ~*~ Domain translation ~*~ #
         @test length(bool_sol) == 4
+        @test size(bool_sol) == (4,)
+        @test size(bool_sol, 1) == 4
         @test length(spin_sol) == 4
+        @test size(spin_sol) == (4,)
+        @test size(spin_sol, 1) == 4
         @test QUBOTools.dimension(bool_sol) == 2
         @test QUBOTools.dimension(spin_sol) == 2
 
@@ -184,13 +188,37 @@ function test_solution_sampleset()
         @test_throws Exception QUBOTools.state(bool_sol, 5)
 
         @test QUBOTools.state(spin_sol, 1) == [↑, ↑]
+        @test_throws Exception QUBOTools.state(spin_sol, 1, 0)
+        @test QUBOTools.state(spin_sol, 1, 1) == ↑
+        @test QUBOTools.state(spin_sol, 1, 2) == ↑
+        @test_throws Exception QUBOTools.state(spin_sol, 1, 3)
+        
         @test QUBOTools.state(spin_sol, 2) == [↑, ↓]
+        @test_throws Exception QUBOTools.state(spin_sol, 2, 0)
+        @test QUBOTools.state(spin_sol, 2, 1) == ↑
+        @test QUBOTools.state(spin_sol, 2, 2) == ↓
+        @test_throws Exception QUBOTools.state(spin_sol, 2, 3)
+
         @test QUBOTools.state(spin_sol, 3) == [↓, ↑]
+        @test_throws Exception QUBOTools.state(spin_sol, 3, 0)
+        @test QUBOTools.state(spin_sol, 3, 1) == ↓
+        @test QUBOTools.state(spin_sol, 3, 2) == ↑
+        @test_throws Exception QUBOTools.state(spin_sol, 3, 3)
+
         @test QUBOTools.state(spin_sol, 4) == [↓, ↓]
+        @test_throws Exception QUBOTools.state(spin_sol, 4, 0)
+        @test QUBOTools.state(spin_sol, 4, 1) == ↓
+        @test QUBOTools.state(spin_sol, 4, 2) == ↓
+        @test_throws Exception QUBOTools.state(spin_sol, 4, 3)
 
         @test_throws Exception QUBOTools.state(spin_sol, 0)
         @test_throws Exception QUBOTools.state(spin_sol, 5)
 
+        # Iteration
+        for (i, s) in enumerate(spin_sol)
+            @test QUBOTools.sample(spin_sol, i) === s
+        end
+
         # ~ reads ~ #
         @test QUBOTools.reads(bool_sol) == 10
         @test QUBOTools.reads(spin_sol) == 10