Writing tests

Being a thoughtfully designed language, Clojure has a built-in unit testing library, namely clojure.test. Apart from that, there are a couple constructs in the core language that are helpful with regard to testing. Of course, these constructs don't allow us to define and run any tests in the formal sense, and the constructs from the clojure.test namespace must be preferred for that purpose.

Let's start off by briefly discussing the constructs from the core language that can be used for unit testing. The assert function checks whether an expression evaluates to a truthy value at runtime. This function will throw an exception if the expression passed to it does not evaluate to a truthy value, and the message of this exception can be optionally specified as a second argument to the assert form. We can effectively disable all the assert forms in a given program by using the global *assert* compile time var. This variable can only be changed by a top-level set! form...