diff --git a/.github/workflows/obvious.yml b/.github/workflows/obvious.yml
index 6e99095..f64d0c0 100644
--- a/.github/workflows/obvious.yml
+++ b/.github/workflows/obvious.yml
@@ -16,4 +16,4 @@ jobs:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
       - run: |
-          bundle exec rspec
+          ruby -Ilib:test test/*_test.rb
diff --git a/Gemfile.lock b/Gemfile.lock
index d259a46..068ec24 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,20 +6,6 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
-    diff-lcs (1.5.0)
-    rspec (3.10.0)
-      rspec-core (~> 3.10.0)
-      rspec-expectations (~> 3.10.0)
-      rspec-mocks (~> 3.10.0)
-    rspec-core (3.10.1)
-      rspec-support (~> 3.10.0)
-    rspec-expectations (3.10.1)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.10.0)
-    rspec-mocks (3.10.2)
-      diff-lcs (>= 1.2.0, < 2.0)
-      rspec-support (~> 3.10.0)
-    rspec-support (3.10.3)
 
 PLATFORMS
   ruby
@@ -28,7 +14,6 @@ PLATFORMS
 
 DEPENDENCIES
   obvious!
-  rspec
 
 BUNDLED WITH
    2.3.4
diff --git a/Rakefile b/Rakefile
index 2995527..c686ef6 100644
--- a/Rakefile
+++ b/Rakefile
@@ -1 +1,9 @@
 require "bundler/gem_tasks"
+require "rake/testtask"
+
+Rake::TestTask.new(:test) do |t|
+  t.libs << "test"
+  t.libs << "lib"
+  t.test_files = FileList['test/**/*_test.rb']
+end
+task :default => :test
diff --git a/obvious.gemspec b/obvious.gemspec
index 30491c6..2f63791 100644
--- a/obvious.gemspec
+++ b/obvious.gemspec
@@ -16,6 +16,4 @@ Gem::Specification.new do |gem|
   gem.executables   = gem.files.grep(%r{^bin/}).map{ |f| File.basename(f) }
   gem.test_files    = gem.files.grep(%r{^(test|spec|features)/})
   gem.require_paths = ["lib"]
-
-  gem.add_development_dependency "rspec"
 end
diff --git a/spec/.spec_helper.rb.swp b/spec/.spec_helper.rb.swp
deleted file mode 100644
index 2e2bda2..0000000
Binary files a/spec/.spec_helper.rb.swp and /dev/null differ
diff --git a/spec/contract_spec.rb b/spec/contract_spec.rb
deleted file mode 100644
index b33bced..0000000
--- a/spec/contract_spec.rb
+++ /dev/null
@@ -1,63 +0,0 @@
-require_relative 'spec_helper'
-require_relative '../lib/obvious/contract'
-
-
-describe Hash do
-  describe '#has_shape?' do
-    it 'should return true for a valid shape' do
-      expect({ id: 1 }.has_shape?(id: Integer)).to be true
-    end
-
-    it 'should return false for an invalid shape' do
-      expect({ id: 1 }.has_shape?(id: String)).to be false
-    end
-
-    it 'should retrn the invalid field if return_field flag is set' do
-      expect({ id: 1 }.has_shape?({id: String}, true)).to eq [false, :id]
-    end
-
-    it 'should allow for nil values to be returned' do
-      expect({ id: nil }.has_shape?({id: String})).to be true
-    end
-  end
-end
-
-class TestContract < Obvious::Contract
-  contract_for :test, {
-    input: { id: Integer },
-    output: { id: Integer, value: String }
-  }
-
-  def test input
-    { id: 1, value: 'this is a test' }
-  end
-end
-
-describe Obvious::Contract do
-
-  describe "#call_method" do
-    it 'should return the correct output for valid input and output shapes' do
-      tc = TestContract.new
-      result = tc.test id: 1
-      expect(result).to eq id: 1, value: 'this is a test'
-    end
-
-    it 'should raise a contract input error with bad input' do
-      tc = TestContract.new
-      expect { tc.test Hash.new }.to raise_error Obvious::ContractInputError
-    end
-
-    it 'should raise a DataNotFound error if {} is returned' do
-      tc = TestContract.new
-      allow(tc).to receive(:test_alias).and_return({})
-      expect { tc.test id: 1 }.to raise_error Obvious::DataNotFoundError
-    end
-
-    it 'should raise a contract output error if nil is returned' do
-      tc = TestContract.new
-      allow(tc).to receive(:test_alias).and_return(nil)
-      expect { tc.test id: 1 }.to raise_error Obvious::ContractOutputError
-    end
-
-  end
-end
diff --git a/spec/entity_spec.rb b/spec/entity_spec.rb
deleted file mode 100644
index eb0fa76..0000000
--- a/spec/entity_spec.rb
+++ /dev/null
@@ -1,75 +0,0 @@
-require_relative '../lib/obvious/entity'
-
-class Thing < Obvious::Entity
-  value :id, Integer 
-  value :name, String 
-end
-
-class Thing2 < Obvious::Entity
-  value :foo , String
-
-  validation :something, Proc.new {
-    if foo != "hello world"
-      msg = "Validation Error: Invalid value for foo, should be 'hello world'"
-      raise Obvious::ValidationError.new msg 
-    end
-  }
-
-  def modify_foo 
-    @values[:foo] = 100
-  end
-
-end
-
-class Thing3 < Obvious::Entity
-  value :foo , String
-
-  validation :something, Proc.new {
-    @values[:foo] = 12
-  }
-
-end
-
-# To test the entity, we are going to use classes that inherit from it instead
-# of poking at it directly. In this case, I think that makes the most sense.
-describe Thing do
-  it 'should create a valid object with valid input' do
-    input = { name: 'Thing', id: 1 }
-    t = Thing.new input
-    expect(t.name).to eq 'Thing'
-    expect(t.id).to eq 1
-  end
-
-  it 'should raise an error with invalid input types' do
-    input = { name: nil, id: nil }
-    expect { Thing.new input }.to raise_error Obvious::TypeError
-  end
-
-  it 'should raise an error with extra fields in input' do
-    input = { name: 'Thing', id: 1, extra: 'should explode' }
-    expect { Thing.new input }.to raise_error Obvious::ShapeError
-  end
-
-  it 'should raise an error when a method tries to modify a value' do
-    t = Thing2.new foo: 'hello world'
-    expect { t.modify_foo }.to raise_error RuntimeError
-  end
-
-  describe '#to_hash' do
-    it 'should return a hash representation of the object' do
-      input = { name: 'Thing', id: 1 }
-      t = Thing.new input
-      expect(t.to_hash).to eq input
-    end
-  end
-
-  describe 'validation' do
-    it 'should raise a validation error on a failed validation' do
-      expect { Thing2.new foo: 'not valid I promise!' }.to raise_error Obvious::ValidationError
-    end
-    
-    it 'should raise an error when trying to modify an object in a validation' do
-      expect { Thing3.new foo: 'hello world' }.to raise_error RuntimeError
-    end
-  end
-end
diff --git a/spec/obj_spec.rb b/spec/obj_spec.rb
deleted file mode 100644
index 08a65a7..0000000
--- a/spec/obj_spec.rb
+++ /dev/null
@@ -1,74 +0,0 @@
-require_relative '../lib/obvious/obj'
-
-class TestObj
-  include Obvious::Obj
-
-  def initialize
-    @local = 'set!'
-  end
-
-  define :defined_method, foo: String, bar: Integer do |input|
-    input
-  end
-
-  define :defined_local do |input|
-    @local
-  end
-
-  define :early_return_example do |input|
-    next true
-    false
-  end
-
-end
-
-describe Obvious::Obj do
-
-  before do
-    @test = TestObj.new
-  end
-
-  describe 'self.define' do
-    it 'should do the right thing with correct input' do
-      result = @test.defined_method foo: 'hello', bar: 12
-      expect(result).to eq foo: 'hello', bar: 12
-    end
-
-    it 'should have access to instance variables' do
-      result = @test.defined_local
-      expect(result).to eq 'set!'
-    end
-
-    it 'should raise an error for missing parameters' do
-      expect { @test.defined_method foo: 'hello' }.to raise_error { |error|
-        expect(error).to be_a ArgumentError
-        expect(error.message).to eq 'missing input field bar'
-      }
-    end
-
-    it 'should raise an error for extra parameters' do
-      expect { @test.defined_method foo: 'hello', bar: 12, extra: 'this is extra!' }.to raise_error { |error|
-        expect(error).to be_a ArgumentError
-        expect(error.message).to eq 'invalid input field extra'
-      }
-    end
-
-    it 'should raise an error for invalid types' do
-      expect { @test.defined_method foo: 1, bar: 12 }.to raise_error { |error|
-        expect(error).to be_a ArgumentError
-        expect(error.message).to eq 'invalid type for foo expected String'
-      }
-
-      expect {@test.defined_method foo: 'hello', bar: nil }.to raise_error { |error|
-        expect(error).to be_a ArgumentError
-        expect(error.message).to eq 'invalid type for bar expected Integer'
-      }
-    end
-
-    it 'should allow for early returns in control flow' do
-      result = @test.early_return_example
-      expect(result).to eq true
-    end
-  end
-
-end
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
deleted file mode 100644
index 0fd1652..0000000
--- a/spec/spec_helper.rb
+++ /dev/null
@@ -1,3 +0,0 @@
-RSpec.configure do |c|
-  c.mock_with :rspec 
-end
diff --git a/test/contract_test.rb b/test/contract_test.rb
new file mode 100644
index 0000000..23de74a
--- /dev/null
+++ b/test/contract_test.rb
@@ -0,0 +1,62 @@
+require 'minitest/autorun'
+require_relative '../lib/obvious/contract'
+
+class TestContract < Obvious::Contract
+  contract_for :test, {
+    input: { id: Integer },
+    output: { id: Integer, value: String }
+  }
+
+  def test input
+    { id: 1, value: 'this is a test' }
+  end
+end
+
+class ContractTest < Minitest::Test
+  def test_valid_input
+    result = TestContract.new.test(id: 1)
+    assert_equal({id: 1, value: 'this is a test'}, result)
+  end
+
+  def test_invalid_input
+    assert_raises Obvious::ContractInputError do
+      TestContract.new.test(Hash.new)
+    end
+  end
+
+  def test_empty_hash_return
+    assert_raises Obvious::DataNotFoundError do
+      tc = TestContract.new
+      tc.stub :test_alias, {} do
+        tc.test(id: 1)
+      end
+    end
+  end
+
+  def test_nil_return
+    assert_raises Obvious::ContractOutputError do
+      tc = TestContract.new
+      tc.stub :test_alias, nil do
+        tc.test(id: 1)
+      end
+    end
+  end
+end
+
+class HashTest < Minitest::Test
+  def test_valid_has_shape
+    assert({id: 1}.has_shape?(id: Integer))
+  end
+
+  def test_invalid_has_shape
+    refute({id: 1}.has_shape?(id: String))
+  end
+
+  def test_has_shape_allow_nil_values
+    assert({id: nil}.has_shape?({id: String}))
+  end
+
+  def test_has_shape_return_invalid_field
+    assert_equal([false, :id], { id: 1 }.has_shape?({id: String}, true))
+  end
+end
diff --git a/test/entity_test.rb b/test/entity_test.rb
new file mode 100644
index 0000000..11e968f
--- /dev/null
+++ b/test/entity_test.rb
@@ -0,0 +1,76 @@
+require 'minitest/autorun'
+require_relative '../lib/obvious/entity'
+
+class Thing < Obvious::Entity
+  value :id, Integer
+  value :name, String
+end
+
+class Thing2 < Obvious::Entity
+  value :foo , String
+
+  validation :something, -> {
+    if foo != "hello world"
+      msg = "Validation Error: Invalid value for foo, should be 'hello world'"
+      raise Obvious::ValidationError.new msg
+    end
+  }
+
+  def modify_foo
+    @values[:foo] = 100
+  end
+end
+
+class Thing3 < Obvious::Entity
+  value :foo , String
+
+  validation :something, -> {
+    @values[:foo] = 12
+  }
+end
+
+
+# Test code begins here
+
+class EntityTest < Minitest::Test
+  def test_valid_input
+    t = Thing.new(name: 'Thing', id: 1)
+    assert_equal('Thing', t.name)
+    assert_equal(1, t.id)
+  end
+
+  def test_invalid_input_types
+    assert_raises Obvious::TypeError do
+      Thing.new(name: nil, id: nil)
+    end
+  end
+
+  def test_invalid_extra_field
+    assert_raises Obvious::ShapeError do
+      Thing.new(name: 'Thing', id: 1, extra: 'should explode')
+    end
+  end
+
+  def test_method_modify_value
+    assert_raises RuntimeError do
+      Thing2.new(foo: 'hello world').modify_foo
+    end
+  end
+
+  def test_to_hash
+    t = Thing.new(name: 'Thing', id: 1)
+    assert_equal({name: 'Thing', id: 1}, t.to_hash)
+  end
+
+  def test_failed_validation
+    assert_raises Obvious::ValidationError do
+      Thing2.new(foo: 'not valid I promise!')
+    end
+  end
+
+  def test_modify_value_inside_validation
+    assert_raises RuntimeError do
+      Thing3.new(foo: 'hello world')
+    end
+  end
+end
diff --git a/test/obj_test.rb b/test/obj_test.rb
new file mode 100644
index 0000000..e4502a4
--- /dev/null
+++ b/test/obj_test.rb
@@ -0,0 +1,65 @@
+require 'minitest/autorun'
+require_relative '../lib/obvious/obj'
+
+class TestObj
+  include Obvious::Obj
+
+  def initialize
+    @local = 'set!'
+  end
+
+  define :defined_method, foo: String, bar: Integer do |input|
+    input
+  end
+
+  define :defined_local do |input|
+    @local
+  end
+
+  define :early_return_example do |input|
+    next true
+    false
+  end
+end
+
+class ObjTest < Minitest::Test
+  def test_valid_input
+    result = TestObj.new.defined_method foo: 'hello', bar: 12
+    assert_equal({foo: 'hello', bar: 12}, result)
+  end
+
+  def test_access_instance_variables
+    result = TestObj.new.defined_local
+    assert_equal('set!', result)
+  end
+
+  def test_missing_parameters
+    error = assert_raises ArgumentError do
+      TestObj.new.defined_method foo: 'hello'
+    end
+    assert_equal('missing input field bar', error.message)
+  end
+
+  def test_extra_parameters
+    error = assert_raises ArgumentError do
+      TestObj.new.defined_method foo: 'hello', bar: 12, extra: 'fail'
+    end
+    assert_equal('invalid input field extra', error.message)
+  end
+
+  def test_invalid_types
+    error = assert_raises ArgumentError do
+      TestObj.new.defined_method foo: 1, bar: 12
+    end
+    assert_equal('invalid type for foo expected String', error.message)
+
+    error = assert_raises ArgumentError do
+      TestObj.new.defined_method foo: 'hello', bar: nil
+    end
+    assert_equal('invalid type for bar expected Integer', error.message)
+  end
+
+  def test_early_return
+    assert(TestObj.new.early_return_example)
+  end
+end