Here User.count is 0 because we reset the database at the beginning of this section.

When submitting invalid data, we expect the user count not to change; when submitting valid data, we expect it to change by 1. We can express this in RSpec by combining the expect method with either the to method or the not_to method. We’ll start with the invalid case since it is simpler; we visit the signup path and click the button, and we expect it not to change the user count:

Note that, as indicated by the curly braces, expect wraps click_button in a block (Section 4.3.2). This is for the benefit of the change method, which takes as arguments an object and a symbol and then calculates the result of calling that symbol as a method on the object both before and after the block. In other words, the code 

calculates

before and after the execution of

In the present case, we want the given code not to change the count, which we express using the not-to method. In effect, by enclosing the button click in a block we are able to replace

with the single line

which reads like natural language and is much more compact.
           The case of valid data is similar, but instead of verifying that the user count doesn’t change, we check that clicking the button changes the count by 1: 

This uses the to method because we expect a click on the signup button with valid data to change the user count by one. Combining the two cases with the appropriate describe blocks and pulling the common code into

          before blocks yields good basic tests for signing up users, as shown in Listing 7.16. Here we’ve factored out the common text for the submit button using the let method to define a submit variable.