1 files changed, 125 insertions, 0 deletions
diff --git a/test/test_singleton.rb b/test/test_singleton.rb
new file mode 100644
index 0000000000..e474a0ccc5
--- /dev/null
+++ b/test/test_singleton.rb
@@ -0,0 +1,125 @@
+# frozen_string_literal: false
+require 'test/unit'
+require 'singleton'
+
+class TestSingleton < Test::Unit::TestCase
+  class SingletonTest
+    include Singleton
+  end
+
+  def test_marshal
+    o1 = SingletonTest.instance
+    m = Marshal.dump(o1)
+    o2 = Marshal.load(m)
+    assert_same(o1, o2)
+  end
+
+  def test_instance_never_changes
+    a = SingletonTest.instance
+    b = SingletonTest.instance
+    assert_same a, b
+  end
+
+  def test_initialize_raises_exception
+    assert_raise NoMethodError do
+      SingletonTest.new
+    end
+  end
+
+  def test_allocate_raises_exception
+    assert_raise NoMethodError do
+      SingletonTest.allocate
+    end
+  end
+
+  def test_clone_raises_exception
+    exception = assert_raise TypeError do
+      SingletonTest.instance.clone
+    end
+
+    expected = "can't clone instance of singleton TestSingleton::SingletonTest"
+
+    assert_equal expected, exception.message
+  end
+
+  def test_dup_raises_exception
+    exception = assert_raise TypeError do
+      SingletonTest.instance.dup
+    end
+
+    expected = "can't dup instance of singleton TestSingleton::SingletonTest"
+
+    assert_equal expected, exception.message
+  end
+
+  def test_include_in_module_raises_exception
+    mod = Module.new
+
+    exception = assert_raise TypeError do
+      mod.class_eval do
+        include Singleton
+      end
+    end
+
+    expected = "Inclusion of the OO-Singleton module in module #{mod}"
+
+    assert_equal expected, exception.message
+  end
+
+  def test_extending_singleton_raises_exception
+    assert_raise NoMethodError do
+      'foo'.extend Singleton
+    end
+  end
+
+  def test_inheritance_works_with_overridden_inherited_method
+    super_super_called = false
+
+    outer = Class.new do
+      define_singleton_method :inherited do |sub|
+        super_super_called = true
+      end
+    end
+
+    inner = Class.new(outer) do
+      include Singleton
+    end
+
+    tester = Class.new(inner)
+
+    assert super_super_called
+
+    a = tester.instance
+    b = tester.instance
+    assert_same a, b
+  end
+
+  def test_inheritance_creates_separate_singleton
+    a = SingletonTest.instance
+    b = Class.new(SingletonTest).instance
+
+    assert_not_same a, b
+  end
+
+  def test_inheritance_instantiation
+    klass = Class.new do
+      include Singleton
+
+      public_class_method :new
+    end
+
+    assert Class.new(klass).new
+  end
+
+  def test_class_level_cloning_preserves_singleton_behavior
+    klass = SingletonTest.clone
+
+    a = klass.instance
+    b = klass.instance
+    assert_same a, b
+  end
+
+  def test_class_level_cloning_creates_separate_singleton
+    assert_not_same SingletonTest.instance, SingletonTest.clone.instance
+  end
+end