Alignment enforces validity of arguments

Had to learn how to raise exceptions and how to expect them in rspec.
Learned about the syntax for writing a setter too, kinda cool.
Also, is it a good approach to define the valid list in the method like
I'm doing? Should that list be a constant somewhere so it doesn't have
to be created each time the method is called? I'm sure it should, but
what's the Ruby Way of doing that?

lib/character.rb

@@ -1,5 +1,14 @@
 class Character
   attr_accessor :name
-  attr_accessor :alignment
+  attr_reader :alignment
+
+  def alignment=(alignment) 
+    valid_alignments = ['Good', 'Evil', 'Neutral']
+    if not valid_alignments.include? alignment.capitalize
+      raise ArgumentError
+    end
+    @alignment = alignment.capitalize
+  end
+
 end
 

spec/character_spec.rb

@@ -14,6 +14,10 @@
     expect(subject.alignment).to eq(expected_alignment)
   end
 
+  it "raises ArgumentError when given an invalid alignment" do
+    expect{subject.alignment = "Decent"}.to raise_error(ArgumentError)
+  end
+
 end