Useful Predicates

Expectations leans heavily on predicates: you can expect any predicate to be true on the (actual) test value. You can use any predicate -- built into Clojure, user-defined, even Specs -- but Expectations also provides a few of its own that can be helpful when checking values are close to some expected result or within an expected range, etc.

approximately

  (expect (approximately 19.99) (default-package-price store))

This checks that the resulting price is "close to" 19.99. By default, approximately uses a "delta" of 0.001 so the above accepts values between 19.989 and 19.991 inclusively. You can provide your own delta value:

  (expect (approximately 100.0 0.5) (total-coverage tests))

This checks that the coverage value is within +/- 0.5 of 100.0 (i.e., 99.5 <= v <= 100.5).

between and between'

Instead of expecting a result to be close to a value, you may expect a result to be within a known range of values. These two predicates offer an inclusive range and an exclusive range respectively.

  ;; (rand-int 10) will produce 0, 1, 2, .., 9
  (expect (between 0 9)    (rand-int 10))
  (expect (between' -1 10) (rand-int 10))
  ;; if you want an inclusive/exclusive range:
  (let [n 100]
    (expect (between 0 (dec n)) (rand-int n)))

functionally

Sometimes you have two functions that you expect to be "functionally equivalent". In other words, when they are given the same argument, they should produce the same value perhaps via different computations. This can also emerge when you have a data structure and a function under test where the result of that function can also be computed via a simple test function for a given set of input data.

Here's a simple example showing that two way to compute the square of a number are "functionally equivalent" (for the given test values):

  (expect (functionally (fn [n] (reduce + (repeat n n)))
                        (fn [n] (* n n)))
          (from-each [i (range 100)]
            i))

Further Reading

• Getting Started
• Collections
• Expecting More
• Expecting Side Effects
• Fixtures & Focused Test Execution