1 files changed, 20 insertions, 7 deletions
diff --git a/spec/ruby/core/array/plus_spec.rb b/spec/ruby/core/array/plus_spec.rb
index 3962b05c39..7ead927fc0 100644
--- a/spec/ruby/core/array/plus_spec.rb
+++ b/spec/ruby/core/array/plus_spec.rb
@@ -14,10 +14,23 @@ describe "Array#+" do
     (ary + ary).should == [1, 2, 3, 1, 2, 3]
   end
 
-  it "tries to convert the passed argument to an Array using #to_ary" do
-    obj = mock('["x", "y"]')
-    obj.should_receive(:to_ary).and_return(["x", "y"])
-    ([1, 2, 3] + obj).should == [1, 2, 3, "x", "y"]
+  describe "converts the passed argument to an Array using #to_ary" do
+    it "successfully concatenates the resulting array from the #to_ary call" do
+      obj = mock('["x", "y"]')
+      obj.should_receive(:to_ary).and_return(["x", "y"])
+      ([1, 2, 3] + obj).should == [1, 2, 3, "x", "y"]
+    end
+
+    it "raises a TypeError if the given argument can't be converted to an array" do
+      -> { [1, 2, 3] + nil }.should.raise(TypeError)
+      -> { [1, 2, 3] + "abc" }.should.raise(TypeError)
+    end
+
+    it "raises a NoMethodError if the given argument raises a NoMethodError during type coercion to an Array" do
+      obj = mock("hello")
+      obj.should_receive(:to_ary).and_raise(NoMethodError)
+      -> { [1, 2, 3] + obj }.should.raise(NoMethodError)
+    end
   end
 
   it "properly handles recursive arrays" do
@@ -32,9 +45,9 @@ describe "Array#+" do
   end
 
   it "does return subclass instances with Array subclasses" do
-    (ArraySpecs::MyArray[1, 2, 3] + []).should be_an_instance_of(Array)
-    (ArraySpecs::MyArray[1, 2, 3] + ArraySpecs::MyArray[]).should be_an_instance_of(Array)
-    ([1, 2, 3] + ArraySpecs::MyArray[]).should be_an_instance_of(Array)
+    (ArraySpecs::MyArray[1, 2, 3] + []).should.instance_of?(Array)
+    (ArraySpecs::MyArray[1, 2, 3] + ArraySpecs::MyArray[]).should.instance_of?(Array)
+    ([1, 2, 3] + ArraySpecs::MyArray[]).should.instance_of?(Array)
   end
 
   it "does not call to_ary on array subclasses" do