Tests to verify failure behavior when an attribute is not included in the readonly set.

spec/shoulda/active_record/have_readonly_attributes_matcher_spec.rb

@@ -15,15 +15,34 @@ describe Shoulda::Matchers::ActiveRecord::HaveReadonlyAttributeMatcher do
     end
   end
 
-  context "an attribute that can be set after being saved" do
+  context "an attribute not included in the readonly set" do
+    before do
+      define_model :example, :attr => :string, :other => :string do
+        attr_readonly :other
+      end
+      @model = Example.new
+    end
+
+    it "should not accept being read-only" do
+      @model.should_not have_readonly_attribute(:attr)
+    end
+  end
+
+  context "an attribute on a class with no readonly attributes" do
     before do
       define_model :example, :attr => :string
       @model = Example.new
     end
 
-    it "should accept being read-only" do
+    it "should not accept being read-only" do
       @model.should_not have_readonly_attribute(:attr)
     end
+
+    it "should assign a failure message" do
+      matcher = have_readonly_attribute(:attr)
+      matcher.matches?(@model).should == false
+      matcher.failure_message.should_not be_nil
+    end
   end
 
 end