OSnap

Random snapshot testing library for OCaml.

The Documentation can be found here. This library uses QCheck generators to generate random values for snapshots.

Build

Build from source:

$ git clone git@github.com:vch9/osnap.git
$ dune build

You can also install with opam:

$ opam install osnap

License

The code is now released under the MIT license.

An introduction to the library

The library intends to test differences on results between two versions.

Binary Exponentiation

Let's say we write a function computing the exponentiation.

let rec exponentiation x n =
  if n = 0 then 1
  else if n = 1 then x
  else exponentiation x (n - 1) * x
  
let test =
  let open Osnap in
  let spec = Spec.(small_int ^> small_int ^>> string_of_int) in
  let path = ".osnap/exponentiation" in
  
  Test.make ~spec ~path ~count:5 ~name:"exponentiation" exponentiation
  
let _ =
 Osnap.Runner.(run_tests ~mode:Interactive [ test ])

In the above, we first provide a naive implementation of the exponentiation. Then, we create a test with the according specification using Osnap combinator.

{
  name = exponentiation;
  scenarios = [
	35	66	=	4292184014870020553
	0	3	=	0
	9	3	=	729
	3	7	=	2187
	67	9	=	27206534396294947
  ]
}

Do you want to promote these diff? [Y\n]

As we agree with our function result, we promote the change by typing Y. We try to improve our function efficiency with binary exponentiation.

let rec binary_expo x n =
  if n = 0 then 1
  else if n mod 2 = 0 then
    let tmp = binary_expo x (n / 2) in
    tmp * tmp
  else x * binary_expo x (n - 1)
  
let test =
  let open Osnap in
  let spec = Spec.(small_int ^> small_int ^>> string_of_int) in
  let path = ".osnap/exponentiation" in

  Test.make ~spec ~path ~count:5 ~name:"exponentiation" binary_expo

let _ = Osnap.Runner.(run_tests ~mode:Interactive [ test ])

Finally, we get the following result:

-------------------------------------------------------------------------------
success: ran 1 test (1 passed)

Osnap has not found any difference between the old and new snapshot ✔️.