diff --git a/.gitignore b/.gitignore
index ce9c3c5..0313bb7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,2 +1,4 @@
 .env
 TODO.md
+.rspec_status
+*.gem
diff --git a/.mdlrc b/.mdlrc
index 68975e8..e350d3d 100644
--- a/.mdlrc
+++ b/.mdlrc
@@ -1 +1 @@
-rules "~MD029", "~MD033", "~MD013"
\ No newline at end of file
+rules "~MD029", "~MD033", "~MD013", "~MD034"
diff --git a/.rspec b/.rspec
new file mode 100644
index 0000000..34c5164
--- /dev/null
+++ b/.rspec
@@ -0,0 +1,3 @@
+--format documentation
+--color
+--require spec_helper
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..3be69e2
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,9 @@
+# Change log
+
+## [master]
+
+## [0.1.0]
+
+- Initial release 👾
+
+[@fargelus]: https://github.com/fargelus
\ No newline at end of file
diff --git a/Gemfile b/Gemfile
index 946445d..d394f1c 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,3 +4,7 @@ source 'https://rubygems.org'
 
 # Specify your gem's dependencies in space_invaders.gemspec
 gemspec
+
+gem 'dotenv'
+gem 'mdl'
+gem 'rspec', '~> 3.0'
diff --git a/Gemfile.lock b/Gemfile.lock
index f9f98f4..ab9c206 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -2,18 +2,20 @@ PATH
   remote: .
   specs:
     space_invaders (0.1.0)
+      gosu
+      mongo (~> 2.2.5)
 
 GEM
   remote: https://rubygems.org/
   specs:
-    bson (4.8.2)
-    byebug (11.1.3)
-    chef-utils (17.9.46)
+    bson (4.15.0)
+    chef-utils (17.10.0)
       concurrent-ruby
-    concurrent-ruby (1.1.9)
-    diff-lcs (1.3)
-    dotenv (2.7.5)
-    kramdown (2.3.1)
+    concurrent-ruby (1.1.10)
+    diff-lcs (1.5.0)
+    dotenv (2.7.6)
+    gosu (1.4.3)
+    kramdown (2.4.0)
       rexml
     kramdown-parser-gfm (1.1.0)
       kramdown (~> 2.0)
@@ -26,39 +28,34 @@ GEM
     mixlib-cli (2.1.8)
     mixlib-config (3.0.9)
       tomlrb
-    mixlib-shellout (3.2.5)
+    mixlib-shellout (3.2.7)
       chef-utils
     mongo (2.2.7)
       bson (~> 4.0)
-    rake (13.0.1)
     rexml (3.2.5)
-    rspec (3.9.0)
-      rspec-core (~> 3.9.0)
-      rspec-expectations (~> 3.9.0)
-      rspec-mocks (~> 3.9.0)
-    rspec-core (3.9.1)
-      rspec-support (~> 3.9.1)
-    rspec-expectations (3.9.1)
+    rspec (3.11.0)
+      rspec-core (~> 3.11.0)
+      rspec-expectations (~> 3.11.0)
+      rspec-mocks (~> 3.11.0)
+    rspec-core (3.11.0)
+      rspec-support (~> 3.11.0)
+    rspec-expectations (3.11.0)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.9.0)
-    rspec-mocks (3.9.1)
+      rspec-support (~> 3.11.0)
+    rspec-mocks (3.11.1)
       diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.9.0)
-    rspec-support (3.9.2)
+      rspec-support (~> 3.11.0)
+    rspec-support (3.11.0)
     tomlrb (2.0.1)
 
 PLATFORMS
-  ruby
+  arm64-darwin-21
 
 DEPENDENCIES
-  bundler (~> 2.0)
-  byebug
   dotenv
   mdl
-  mongo (~> 2.2.5)
-  rake (~> 13.0)
   rspec (~> 3.0)
   space_invaders!
 
 BUNDLED WITH
-   2.1.4
+   2.3.9
diff --git a/lib/space_invaders/aliens.rb b/lib/space_invaders/aliens.rb
index a53d81f..5195176 100644
--- a/lib/space_invaders/aliens.rb
+++ b/lib/space_invaders/aliens.rb
@@ -109,10 +109,10 @@ def above_enemy_alien
       closest = find(@enemy.x + @enemy.w)
       return closest if closest
 
-      further_x = last_column_x(@aliens)
+      further_x = max_x_coord(@aliens)
       return find(further_x) if further_x < @enemy.x
 
-      find(first_column_x(@aliens))
+      find(min_x_coord(@aliens))
     end
 
     def can_move?
@@ -146,8 +146,8 @@ def next_move_direction
     def available_directions
       extreme_right_aliens = WIDTH - ALIENS_WIDTH - ALIENS_MARGIN
       {
-        right: first_column_x(@aliens) < ALIENS_MARGIN,
-        left: last_column_x(@aliens) > extreme_right_aliens
+        right: min_x_coord(@aliens) < ALIENS_MARGIN,
+        left: max_x_coord(@aliens) > extreme_right_aliens
       }
     end
 
diff --git a/lib/space_invaders/base/helpers.rb b/lib/space_invaders/base/helpers.rb
index f049c90..43b4982 100644
--- a/lib/space_invaders/base/helpers.rb
+++ b/lib/space_invaders/base/helpers.rb
@@ -5,15 +5,11 @@
 
 module SpaceInvaders
   module Helpers
-    def horizontal_center(obj)
-      Settings::WIDTH / 2 - obj.w / 2
-    end
-
-    def last_column_x(collection)
+    def max_x_coord(collection)
       collection.max_by(&:x).x
     end
 
-    def first_column_x(collection)
+    def min_x_coord(collection)
       collection.min_by(&:x).x
     end
   end
diff --git a/space_invaders.gemspec b/space_invaders.gemspec
index 4acfd53..0e02b32 100644
--- a/space_invaders.gemspec
+++ b/space_invaders.gemspec
@@ -14,25 +14,18 @@ Gem::Specification.new do |spec|
   spec.description   = 'Space Invaders classic 2d game'
   spec.homepage      = 'https://github.com/fargelus/space-invaders'
   spec.license       = 'MIT'
-
-  spec.metadata['allowed_push_host'] = "TODO: Set to 'http://mygemserver.com'"
+  spec.required_ruby_version = '>= 2.6.0'
 
   spec.metadata['homepage_uri'] = spec.homepage
+  spec.metadata['changelog_uri'] = 'https://github.com/fargelus/space-invaders/CHANGELOG.md'
 
   # Specify which files should be added to the gem when it is released.
-  # The `git ls-files -z` loads the files in the RubyGem that have been added into git.
-  spec.files = Dir.chdir(File.expand_path(__dir__)) do
-    `git ls-files -z`.split("\x0").reject { |f| f.match(%r{^(test|spec|features)/}) }
-  end
-  spec.bindir        = 'exe'
-  spec.executables   = spec.files.grep(%r{^exe/}) { |f| File.basename(f) }
+  spec.files = Dir.glob('lib/**/*') + Dir.glob('bin/**/*') + %w[README.md CHANGELOG.md]
+  spec.bindir        = 'bin'
+  spec.executables   = 'space_invaders'
   spec.require_paths = ['lib']
 
-  spec.add_development_dependency 'bundler', '~> 2.0'
-  spec.add_development_dependency 'dotenv'
-  spec.add_development_dependency 'byebug'
-  spec.add_development_dependency 'mongo', '~> 2.2.5'
-  spec.add_development_dependency 'rake', '~> 13.0'
-  spec.add_development_dependency 'rspec', '~> 3.0'
-  spec.add_development_dependency 'mdl'
+  spec.add_dependency 'gosu'
+  # TODO Change to SQLite
+  spec.add_dependency 'mongo', '~> 2.2.5'
 end
diff --git a/spec/base/helpers_spec.rb b/spec/base/helpers_spec.rb
new file mode 100644
index 0000000..b16ce34
--- /dev/null
+++ b/spec/base/helpers_spec.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+require 'space_invaders/base/helpers'
+require 'ostruct'
+
+RSpec.describe SpaceInvaders::Helpers do
+  include SpaceInvaders::Helpers
+
+  let(:collection) do
+    [
+      OpenStruct.new(x: 2, y: 35),
+      OpenStruct.new(x: 50, y: 0),
+      OpenStruct.new(x: -100, y: 200)
+    ]
+  end
+
+  describe '#max_x_coord' do
+    subject { max_x_coord(collection) }
+
+    it 'returns max x value' do
+      expect(subject).to eql 50
+    end
+  end
+
+  describe '#min_x_coord' do
+    subject { min_x_coord(collection) }
+
+    it 'returns min x value' do
+      expect(subject).to eql(-100)
+    end
+  end
+end
diff --git a/spec/base/image_object_spec.rb b/spec/base/image_object_spec.rb
new file mode 100644
index 0000000..ec55e58
--- /dev/null
+++ b/spec/base/image_object_spec.rb
@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+require 'space_invaders/base/image_object'
+
+RSpec.describe SpaceInvaders::ImageObject do
+  let(:image_path) { File.join(Dir.pwd, 'spec', 'fixtures', 'files', 'ruby.png') }
+
+  subject(:image_object) { described_class.new(0, 0, image_path) }
+
+  describe '#set' do
+    before { image_object.set(100, 200) }
+
+    it 'updates x and y coordinates' do
+      expect(image_object.x).to eql 100
+      expect(image_object.y).to eql 200
+    end
+  end
+
+  describe '#draw' do
+    before do
+      allow_any_instance_of(Gosu::Image).to receive(:draw).and_return nil
+    end
+
+    it 'draws an image at predefined coords' do
+      expect_any_instance_of(Gosu::Image).to receive(:draw).with(0, 0, 0)
+      image_object.draw
+    end
+  end
+end
diff --git a/spec/fixtures/files/ruby.png b/spec/fixtures/files/ruby.png
new file mode 100644
index 0000000..9d88d4d
Binary files /dev/null and b/spec/fixtures/files/ruby.png differ
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index c6aed2f..e900f0a 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -1,7 +1,6 @@
 # frozen_string_literal: true
 
 require 'bundler/setup'
-require 'space_invaders'
 
 RSpec.configure do |config|
   # Enable flags like --only-failures and --next-failure
diff --git a/spec/space_invaders_spec.rb b/spec/version_spec.rb
similarity index 69%
rename from spec/space_invaders_spec.rb
rename to spec/version_spec.rb
index b6b2f27..59946c2 100644
--- a/spec/space_invaders_spec.rb
+++ b/spec/version_spec.rb
@@ -1,11 +1,9 @@
 # frozen_string_literal: true
 
+require 'space_invaders/version'
+
 RSpec.describe SpaceInvaders do
   it 'has a version number' do
     expect(SpaceInvaders::VERSION).not_to be nil
   end
-
-  it 'does something useful' do
-    expect(false).to eq(true)
-  end
 end