diff --git a/app/models/block.rb b/app/models/block.rb
index 5d52a14..b0f137d 100644
--- a/app/models/block.rb
+++ b/app/models/block.rb
@@ -1,2 +1,10 @@
 class Block < ActiveRecord::Base
+  belongs_to :box
+
+  #<tt>position</tt> codl not be nil and must be an integer
+  validates_numericality_of :position, :only_integer => true , :message => _('%{fn} must be composed only of integers')
+
+  # A block must be associated to a box
+  validates_presence_of :box_id 
+
 end
diff --git a/app/models/box.rb b/app/models/box.rb
index 8e489df..ea414cb 100644
--- a/app/models/box.rb
+++ b/app/models/box.rb
@@ -2,8 +2,8 @@ class Box < ActiveRecord::Base
   belongs_to :owner, :polymorphic => true
 
   #we cannot have two boxs with the same number to the same owner
-  validates_uniqueness_of :number, :scope => :owner
+  validates_uniqueness_of :number, :scope => [:owner_type, :owner_id]
 
-  #<tt>number</tt> must be a integer
+  #<tt>number</tt> could not be nil and must be an integer
   validates_numericality_of :number, :only_integer => true, :message => _('%{fn} must be composed only of integers.')
 end
diff --git a/app/models/user.rb b/app/models/user.rb
index 4a57cf0..8d33177 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -1,2 +1,3 @@
 class User < ActiveRecord::Base
+  has_many :boxes, :as => :owner
 end
diff --git a/test/fixtures/boxes.yml b/test/fixtures/boxes.yml
index c786b5e..953874e 100644
--- a/test/fixtures/boxes.yml
+++ b/test/fixtures/boxes.yml
@@ -2,9 +2,15 @@
 one:
   id: 1
   number: 1
+  owner_type: 'User'
+  owner_id: 1
 two:
   id: 2
   number: 2
+  owner_type: 'User'
+  owner_id: 1
 three:
   id: 3
   number: 3
+  owner_type: 'User'
+  owner_id: 1
diff --git a/test/fixtures/users.yml b/test/fixtures/users.yml
new file mode 100644
index 0000000..7316778
--- /dev/null
+++ b/test/fixtures/users.yml
@@ -0,0 +1,7 @@
+# Read about fixtures at http://ar.rubyonrails.org/classes/Fixtures.html
+one:
+  id: 1
+  name: 'Leandro Nunes dos Santos'
+two:
+  id: 2
+  name: 'Antonio S. A. Terceiro'
diff --git a/test/unit/block_test.rb b/test/unit/block_test.rb
index 83c97a9..ffe2355 100644
--- a/test/unit/block_test.rb
+++ b/test/unit/block_test.rb
@@ -4,7 +4,55 @@ class BlockTest < Test::Unit::TestCase
   fixtures :blocks
 
   # Replace this with your real tests.
-  def test_truth
-    assert true
+  def test_create
+    count = Block.count 
+    b = Block.new
+    assert !b.valid?
+    assert b.errors.invalid?(:box_id)
+    assert b.errors.invalid?(:position)
+    
+    u = User.new
+    assert u.save
+    box = Box.new
+    box.owner = u 
+    box.number = 1000
+    assert box.save
+    b.box = box
+    assert !b.valid?
+    assert b.errors.invalid?(:position)
+
+    b.position=1
+    assert b.save
+
+    assert_equal count + 1, Block.count
+  end
+
+  def test_box_presence
+    b = Block.new
+    b.position = 1000
+    assert !b.valid?
+    assert b.errors.invalid?(:box_id)
+
+    u = User.new
+    assert u.save
+    box = Box.new
+    box.owner = u 
+    box.number = 1000
+    assert box.save
+    b.box = box
+    assert b.valid?
+
   end
+
+  def test_destroy
+    b = Block.find(1)
+    assert b.destroy 
+  end
+
+  def test_valid_fixtures
+    Block.find_all.each do |b|
+      assert b.valid?
+    end
+  end
+
 end
diff --git a/test/unit/box_test.rb b/test/unit/box_test.rb
index c42e14e..31dc94c 100644
--- a/test/unit/box_test.rb
+++ b/test/unit/box_test.rb
@@ -43,4 +43,10 @@ class BoxTest < Test::Unit::TestCase
     assert b.errors.invalid?(:number)
   end
 
+  def test_presence_number
+    b = Box.new(:number => nil)
+    assert !b.valid?
+    assert b.errors.invalid?(:number)
+  end
+
 end
--
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