1 files changed, 74 insertions, 0 deletions
diff --git a/spec/ruby/core/kernel/singleton_class_spec.rb b/spec/ruby/core/kernel/singleton_class_spec.rb
new file mode 100644
index 0000000000..23c400f9bd
--- /dev/null
+++ b/spec/ruby/core/kernel/singleton_class_spec.rb
@@ -0,0 +1,74 @@
+# truffleruby_primitives: true
+require_relative '../../spec_helper'
+
+describe "Kernel#singleton_class" do
+  it "returns class extended from an object" do
+    x = Object.new
+    xs = class << x; self; end
+    xs.should == x.singleton_class
+  end
+
+  it "returns NilClass for nil" do
+    nil.singleton_class.should == NilClass
+  end
+
+  it "returns TrueClass for true" do
+    true.singleton_class.should == TrueClass
+  end
+
+  it "returns FalseClass for false" do
+    false.singleton_class.should == FalseClass
+  end
+
+  it "raises TypeError for Integer" do
+    -> { 123.singleton_class }.should raise_error(TypeError, "can't define singleton")
+  end
+
+  it "raises TypeError for Float" do
+    -> { 3.14.singleton_class }.should raise_error(TypeError, "can't define singleton")
+  end
+
+  it "raises TypeError for Symbol" do
+    -> { :foo.singleton_class }.should raise_error(TypeError, "can't define singleton")
+  end
+
+  it "raises TypeError for a frozen deduplicated String" do
+    -> { (-"string").singleton_class }.should raise_error(TypeError, "can't define singleton")
+    -> { a = -"string"; a.singleton_class }.should raise_error(TypeError, "can't define singleton")
+    -> { a = "string"; (-a).singleton_class }.should raise_error(TypeError, "can't define singleton")
+  end
+
+  it "returns a frozen singleton class if object is frozen" do
+    obj = Object.new
+    obj.freeze
+    obj.singleton_class.frozen?.should be_true
+  end
+
+  context "for an IO object with a replaced singleton class" do
+    it "looks up singleton methods from the fresh singleton class after an object instance got a new one" do
+      proxy = -> io { io.foo }
+      if RUBY_ENGINE == 'truffleruby'
+        # We need an inline cache with only this object seen, the best way to do that is to use a Primitive
+        sclass = -> io { Primitive.singleton_class(io) }
+      else
+        sclass = -> io { io.singleton_class }
+      end
+
+      io = File.new(__FILE__)
+      io.define_singleton_method(:foo) { "old" }
+      sclass1 = sclass.call(io)
+      proxy.call(io).should == "old"
+
+      # IO#reopen is the only method which can replace an object's singleton class
+      io2 = File.new(__FILE__)
+      io.reopen(io2)
+      io.define_singleton_method(:foo) { "new" }
+      sclass2 = sclass.call(io)
+      sclass2.should_not.equal?(sclass1)
+      proxy.call(io).should == "new"
+    ensure
+      io2.close
+      io.close
+    end
+  end
+end