Power Assertion macro for Clojure

The Power Assertions feature in the Groovy language is a strong tool, it makes writing tests and finding bugs easier. This is an implementation for the Clojure programming language with support for macros and lazy sequences.

It prints subexpressions on assert failure.

And each evaluations of subexpressions are shown.

Usage

This library provides four small macros for easier debugging.

• The examine macro can be used to trace parts of an evaluated expression. Debug information is printed to the standard output and the value of the expression is returned.
• The assert macro is similar to clojure.core/assert. It wraps the examined information in the thrown AssertionError instance.
• The verify macro is just like assert, but it throws an ExceptionInfo instead.
• The is macro is a drop-in replacement for clojure.test/is for unit tests.

First, add the dependency to your project.clj.

[io.github.erdos/erdos.assert "0.2.1"]

Second, require the namespace:

(require '[erdos.assert :as ea])

In the REPL, examining simple expressions will print to *out*.

erdos.assert=> (examine (* (+ 19 17) (- 19 17)))

(* (+ 19 17) (- 19 17))
¦  ¦         ¦
72 36        2

You can also write assertions that will wrap examined data as a string in the AssertionError instance.

erdos.assert=> (assert (= 1 (* 3 (/ 1 3)) "") ; does not print anything

erdos.assert=> (assert (= (* 1.0 1) (* 3 (/ 1 3))) "")

; AssertionError
; (= (* 1.0 1) (* 3 (/ 1 3)))
; ¦  ¦         ¦    ¦
; ¦  1.0       1N   1/3
; false

Shown output is arranged to make place for more complex output.

erdos.assert=> (examine (+ (* 12 (- 32 12) 12.2) (- 3 (/ 1 2 3 4) 2.2) (* (- 1 2) 3)))

(+ (* 12 (- 32 12) 12.2) (- 3 (/ 1 2 3 4) 2.2) (* (- 1 2) 3))
¦  ¦     ¦               ¦    ¦                ¦  ¦
¦  ¦     20              ¦    1/24             -3 -1
¦  2928.0                0.7583333333333329
2925.758333333333

Some expressions are evaluated repeatedly, hence all values are shown.

erdos.assert=> (examine (dotimes [i 5] (print (* i i))))

(dotimes [i 5] (print (* i i)))
               ¦      ¦
               ¦      16, 9, 4, 1, 0
               nil, nil, nil, nil, nil

Only the already realized part is printed for lazy sequences.

erdos.assert=> (examine (reduce + (map * (range) (range 0 10 2))))

(reduce + (map * (range) (range 0 10 2)))
¦         ¦      ¦       ¦
60        (…)    (0 …)   (0 2 4 6 8) 

In such cases you might want to run doall on intermediate lazy sequences.

erdos.assert=> (examine (reduce + (doall (map * (range) (range 0 10 2)))))

(reduce + (doall (map * (range) (range 0 10 2))))
¦         ¦      ¦      ¦       ¦
60        ¦      (…)    (0 …)   (0 2 4 6 8) 
          (0 2 8 18 32) 

Add the ^:show metadata to function arguments to show the values on every function invocation:

erdos.assert=> (examine (mapv (fn [^:show a] (mod a 3)) (range 10)))

(mapv (fn [a] (mod a 3)) (range 10))
¦          ¦  ¦          ¦
¦          ¦  ¦          (0 1 2 3 4 5 6 7 8 9)
¦          ¦  0, 1, 2, 0, 1, 2, 0, 1, 2, 0
¦          0, 1, 2, 3, 4, 5, 6, 7, 8, 9
[0 1 2 0 1 2 0 1 2 0]

License

Copyright © 2017-2021 Janos Erdos

Distributed under the Eclipse Public License version 1.0.