diff --git a/lib/rock.ex b/lib/rock.ex
index 4e033fc..320ed59 100644
--- a/lib/rock.ex
+++ b/lib/rock.ex
@@ -1,6 +1,8 @@
 defmodule Rock do
+  alias Rock.Utils
+  alias Rock.Algorithm
   @moduledoc """
-  Documentation for Rock.
+  ROCK: A Robust Clustering Algorithm for Categorical Attributes
   """
 
   @doc """
@@ -12,7 +14,14 @@ defmodule Rock do
       :world
 
   """
-  def hello do
-    :world
+
+  def clusterize(points, number_of_clusters, theta, similarity_function \\ nil)
+      when is_list(points)
+      when is_number(number_of_clusters)
+      when is_number(theta) do
+    points
+    |> Utils.internalize_points
+    |> Algorithm.clusterize(number_of_clusters, theta, similarity_function)
+    |> Utils.externalize_clusters
   end
 end
diff --git a/lib/rock/algorithm.ex b/lib/rock/algorithm.ex
index b2ee185..a3e5692 100644
--- a/lib/rock/algorithm.ex
+++ b/lib/rock/algorithm.ex
@@ -2,11 +2,15 @@ defmodule Rock.Algorithm do
   alias Rock.Struct.Cluster
   alias Rock.NeighbourCriterion
   alias Rock.Links
-  alias Rock.ClusterMergeCriterion
   alias Rock.Heaps
 
-  def clusterize(points, number_of_clusters, theta) when is_list(points) do
-    neighbour_criterion = theta |> NeighbourCriterion.new
+  def clusterize(points, number_of_clusters, theta, similarity_function \\ nil) when is_list(points) do
+    neighbour_criterion = if is_nil(similarity_function) do
+        theta |> NeighbourCriterion.new
+      else
+        theta |> NeighbourCriterion.new(similarity_function)
+      end
+
     link_matrix = points |> Links.matrix(neighbour_criterion)
     initial_clusters = points |> initialize_clusters
     current_number_of_clusters = points |> Enum.count
@@ -30,6 +34,12 @@ defmodule Rock.Algorithm do
     end)
   end
 
+  defp optimize_clusters(_, _, _, necessary_number, current_number)
+      when necessary_number > current_number do
+
+    raise ArgumentError, message: "Needed number of clusters must be smaller than number of points"
+  end
+
   defp optimize_clusters(_, clusters, _, necessary_number, current_number)
       when necessary_number == current_number do
     clusters
@@ -39,7 +49,7 @@ defmodule Rock.Algorithm do
     global_heap = local_heaps |> Heaps.global_heap
     {_, _, v_uuid, u_uuid} = global_heap |> Enum.at(0)
     v_cluster = clusters |> find_cluster(v_uuid)
-    u_cluster = clusters  |> find_cluster(u_uuid)
+    u_cluster = clusters |> find_cluster(u_uuid)
 
     {new_local_heap, new_cluster} =
       local_heaps
diff --git a/mix.exs b/mix.exs
index 6ec095c..1aadb6b 100644
--- a/mix.exs
+++ b/mix.exs
@@ -20,10 +20,11 @@ defmodule Rock.Mixfile do
     [
       {:credo, "~> 0.7", only: [:dev, :test]},
       {:uuid, "~> 1.1"},
-      {:apex, "~>1.0.0", only: [:dev, :test]}
+      {:apex, "~> 1.0.0", only: [:dev, :test]}
     ]
   end
 
   defp elixirc_paths(:test), do: ["lib", "test/support"]
   defp elixirc_paths(_), do: ["lib"]
 end
+
diff --git a/test/rock_test.exs b/test/rock_test.exs
index d379348..03ba383 100644
--- a/test/rock_test.exs
+++ b/test/rock_test.exs
@@ -1,8 +1,67 @@
 defmodule RockTest do
   use ExUnit.Case
-  doctest Rock
 
-  test "the truth" do
-    assert 1 + 1 == 2
+  alias Rock.Struct.Point 
+
+  @points  [
+    {"point1", ["1", "2", "3"]},
+    {"point2", ["1", "2", "4"]},
+    {"point3", ["1", "2", "5"]},
+    {"point4", ["1", "3", "4"]},
+    {"point5", ["1", "3", "5"]},
+    {"point6", ["1", "4", "5"]},
+    {"point7", ["2", "3", "4"]},
+    {"point8", ["2", "3", "5"]},
+    {"point9", ["2", "4", "5"]},
+    {"point10", ["3", "4", "5"]},
+    {"point11", ["1", "2", "6"]},
+    {"point12", ["1", "2", "7"]},
+    {"point13", ["1", "6", "7"]},
+    {"point14", ["2", "6", "7"]}
+  ]
+
+  test "clusterizes points" do
+    theta = 0.15
+    number_of_clusters = 2
+
+    result = @points |> Rock.clusterize(number_of_clusters, theta)
+
+    [
+      [
+        ["1", "2", "6"],
+        ["1", "2", "7"],
+        ["1", "3", "5"],
+        ["1", "4", "5"],
+        ["1", "2", "5"],
+        ["1", "3", "4"],
+        ["1", "2", "3"],
+        ["1", "2", "4"],
+        ["2", "3", "4"],
+        ["2", "3", "5"],
+        ["2", "4", "5"],
+        ["3", "4", "5"]
+      ],
+      [
+        ["1", "6", "7"],
+        ["2", "6", "7"]
+      ]
+    ] = result
+  end
+
+  test "clusterizes points with custom similarity function" do
+    theta = 0.5
+    number_of_clusters = 2
+    similarity_function = fn(
+        %Point{attributes: attributes1},
+        %Point{attributes: attributes2}) ->
+      count1 = Enum.count(attributes1)
+      count2 = Enum.count(attributes2)
+
+      if count1 >= count2, do: count2 / count1, else: count1 / count2
+    end
+
+    result = @points |> Rock.clusterize(number_of_clusters, theta, similarity_function)
+
+    ^number_of_clusters = result |> Enum.count
   end
 end