+ + Instance double over double + +
+ +Instance double ensures the object responds to methods being called, which is not true for double.
+ +
+{% highlight ruby %}
+class User
+ def full_name
+ "#{first_name} #{last_name}"
+ end
+end
+{% endhighlight %}
+
+
+
+{% highlight ruby %}
+it "passes" do
+ user = double(:user, name: "Ayrton Senna")
+ puts user.name
+end
+{% endhighlight %}
+
+
+
+{% highlight ruby %}
+it "fails" do
+ user = instance_double(User, name: "Ayrton Senna")
+ puts user.name
+end
+{% endhighlight %}
+
+
+ The above test will fail with the following message since the name method really doesn't exist.
+{% highlight text %}
+the User class does not implement the instance method: name. Perhaps you meant to use `class_double` instead?
+{% endhighlight %}
+
+