Kaputt is a unit testing tool for the OCaml language1. Its name stems from the following acronym: Kaputt is A Popperian Unit Testing Tool. The adjective popperian is derived from the name of Karl Popper, a famous philosopher of science who is known for forging the concept of falsifiability. The tribute to Popper is due to the fact that Kaputt, like most test-based methodologies, will never tell you that your function is correct; it can only point out errors.
Kaputt features two main kinds of tests:
When writing assertion-based tests, the developer explicitly encodes input values and checks that output values satisfy given assertions. When writing specification-based tests, the developer encodes the specification of the tested function and then requests the library to either generate random values, or enumerate values to be tested against the specification.
Kaputt also provides shell-based tests that barely execute commands such as grep, diff, etc. They can be regarded as a special kind of assertion-based tests, and can be useful to run the whole application and compare its output to reference runs whose output has been stored into files.
Kaputt is distributed under the terms of the gpl version 3. This licensing scheme should not cause any problem, as test versions of applications are intended to be used during development but should not be released publicly.
In order to improve the project, I am primarily looking for testers and bug reporters. Pointing errors in documentation and indicating where it should be enhanced is also very helpful.
Bugs and feature requests can be made at http://bugs.x9c.fr.
Other requests can be sent to firstname.lastname@example.org.
Before starting to build Kaputt, one first has to check that dependencies are already installed. The following elements are needed in order to build Kaputt:
The configuration of Argot is done by executing ./configure. One can specify elements if they are not correctly inferred by the configure script; the following switches are available:
The Java2 version will be built only if the ocamljava3 compiler is present and located by the makefile. The syntax extension will be compiled only to bytecode.
The actual build of Kaputt is launched by executing make all. When build is finished, it is possible to run some simple tests by running make tests. Documentation can be generated by running make doc.
Kaputt is installed by executing make install. According to local settings, it may be necessary to acquire privileged accesses, running for example sudo make install. The actual installation directory depends on the use of ocamlfind: if present the files are placed inside the Findlib hierarchy, otherwise they are placed in the directory ‘ocamlc -where‘/kaputt (i. e. $PREFIX/lib/ocaml/kaputt).
To use Kaputt, it is sufficient to compile and link with the library. This is usually done by adding of the following to the compiler invocation:
Since version 1.0, to access bigarray- and num-specific elements, it is necessary to link with respectively kaputtBigarray.cm[oxj] and kaputtNums.cm[oxj].
Typically, the developer wants to compile the code for tests only for internal (test) versions, and not for public (release) versions. Hence the need to be able to build two versions. The IFDEF directive of camlp4 can be used to fulfill this need. Code sample 3.1 shows a trivial program that is designed to be compiled either to debug or to release mode.
let () = IFDEF DEBUG THEN print_endline "debug mode on" ELSE print_endline "debug mode off" ENDIF
To compile the debug version, one of the following commands (according to the compiler used) should be issued:
At the opposite, to compile the release version, one of following commands should be executed:
This means that the developer can choose the version to compile by only specifying a different preprocessor (precisely by enabling/disabling a preprocessor argument) to be used by the invoked OCaml compiler.
Code sample 3.2 shows how to use Kaputt from a toplevel session. First, the Kaputt directory is added to the search path. Then, the library is loaded and the module containing shorthand definitions is opened. Finally, the check method is used in order to check that the successor of an odd integer is even.
OCaml version 4.00.0 # #directory "+kaputt";; # #load "kaputt.cma";; # open Kaputt.Abbreviations;; # check Gen.int succ [Spec.is_odd_int ==> Spec.is_even_int];; Test 'untitled no 1' ... 100/100 cases passed - : unit = () #
Since version 1.2, it is possible to use a preprocessor (named kaputt_pp.byte) in order to store tests in .mlt files. The underlying idea is to use the file mod.mlt to store the tests for the module Mod whose implementation is in file mod.ml. The preprocessor just appends the contents of mod.mlt to mod.ml when the compiler processes the file mod.ml. If no .mlt file is found alongside the .ml file, the preprocessor does nothing.
The kaputt_pp.byte should always be invoked with a first parameter either equal to on or off, indicating whether concatenation of .ml and .mlt files should occur. The other parameters should indicate which preprocessor to use for the .ml file, leading to a command-line with the following form:
This way of organizing tests is useful because is allows to simultaneously:
When using the preprocessor while compiling with the ocamlbuild tool, one has to be cautious and not to forget to copy .mlt files into the build directory of ocamlbuild. Assuming that all source files are in the src directory and its subdirectories, this can be done through the ocamlbuild plugin shown by code sample 3.3. Then, it is sufficient to tag files with the kaputt tag defined by the plugin with a line such as <src/**/*.ml>: kaputt in the _tags file.
open Ocamlbuild_plugin open Ocamlbuild_pack let rec copy_mlt_files path = let elements = Pathname.readdir path in Array.iter (fun p -> if Pathname.is_directory (path / p) then copy_mlt_files (path / p) else if Pathname.check_extension p "mlt" then let src = path / p in let dst = !Options.build_dir / path / p in Shell.mkdir_p (!Options.build_dir / path); Pathname.copy src dst else ()) elements let () = dispatch begin function | After_rules -> copy_mlt_files "src"; flag ["kaputt"; "pp"] (S [A"kaputt_pp.byte"; A"on"; A"camlp4o"]) | _ -> () end
When writing assertion-based tests, one is mainly interested in the Assertion and Test modules. The Assertion module provides various functions performing tests over values. Then, the Test module allows to run the tests and get some report about their outcome. An assertion-based test built by the Test.make_assert_test function is made of four elements:
The idea of the set up and tear down functions is that they bracket the execution of the tested function. If there is no data to pass to the test function (i.e. its signature is unit -> unit), the obvious choices for set up and tear down are respectively Test.return () and ignore; another possibility is to use the make_simple_test function. Code sample 4.1 shows a short program declaring and running two tests, the first one uses no data while the second one does. The second test also exhibits the fact that the title is optional.
open Kaputt.Abbreviations let t1 = Test.make_simple_test ~title:"first test" (fun () -> Assert.equal_int 3 (f 2)) let t2 = Test.make_assert_test (fun () -> open_in "data") (fun ch -> Assert.equal_string "waited1" (f1 ch); ch) close_in_noerr let () = Test.run_tests [t1; t2]
Mock functions may be useful when writing assertion-based tests. Mock functions are functions that can be created from usual functions, from ⟨ input, output ⟩ couples, or from ⟨ input, output ⟩ sequences. They also record all the calls made to the function, allowing to check if the function has been used as expected. Code sample 4.2 shows how to write an assertion-based test for the List.map function, ensuring that the higher-order function is called on each element of the passed list from left to right.
open Kaputt.Abbreviations let () = Test.add_simple_test (fun () -> let eq_int_list = Assert.make_equal_list (=) string_of_int in let f = Mock.from_function succ in let i = [0; 1; 2; 0] in let o = List.map (Mock.func f) i in let o' = [1; 2; 3; 1] in eq_int_list o' o; eq_int_list i (Mock.calls f); Assert.equal_int 4 (Mock.total f))
When writing specification-based tests, one is mainly interested in the Generator, Specification, and Test modules. The Generator module defines the concept of generator that is a function randomly producing values of a given type, and provides implementations for basic types and combinators. The Specification module defines the concept of specification that is predicates over values and their images through the tested function, as well as predicates over basic types and combinators. A specification-based test built by Test.make_random_test is made of nine elements (the six first ones being optional):
The generator, of type ’a Generator.t, is used to randomly produce test cases. Tests cases are produced until the requested number has be reached. One should notice that a test case is counted if and only if the generated value satisfies one of the preconditions of the specification.
The classifier is used to characterize the generated test cases to give the developer an overview of the coverage of the test (in the sense that the classifier gives hints about the portions of code actually executed). For complete coverage information, one is advised to use the Bisect tool2 by the same author.
The specification is a list of ⟨precondition, postcondition⟩ couples. This list should be regarded as a case-based definition. When checking if the function matches its specification, Kaputt will determine the first precondition from the list that holds, and ensure that the corresponding postcondition holds: if not, a counterexample has been found.
Assuming that the tested function has a signature of ’a -> ’b, a precondition has type ’a predicate (that is ’a -> bool) and a postcondition has type (’a * ’b) predicate (that is (’a * ’b) -> bool). The preconditions are evaluated over the generated values, while the postconditions are evaluated over ⟨generated values, image by tested function⟩ couples.
An easy way to build ⟨precondition, postcondition⟩ couples is to use the => infix operator. Additionally, the ==> infix operator can be used when the postcondition is interested only in the image through the function (ignoring the generated value), thus enabling lighter notation.
Code sample 5.1 shows how to build a test for function f whose domain is the string type. The classifier stores generated values into two categories, according to the length of the string. The pre_i functions are of type string -> bool, while the post_i functions are of type (string * t) -> bool where t is the codomain (also sometimes referred to as the “range”) of the tested function f.
open Kaputt.Abbreviations let t = Test.make_random_test ~title:"random test" ~nb_runs:128 ~classifier:(fun s -> if (String.length s) < 4 then "short" else "long") (Gen.string (Gen.make_int 0 16) Gen.char) f [ pre_1 => post_1 ; ... pre_n => post_n ] let () = Test.run_test t
It is also possible to write specification for partial function, and to check then though xyz_partial functions. Partial functions have a codomain type that is ’b outcome rather than simply ’b. The Specification.outcome type is a sum type with two constructors: Result of ’b, and Exception of exn. The Specification module provides two combinators is_exception and is_result that allow to respectively test an exceptional result and a normal result. Code sample 5.2 tests that the tested f function (of type
int -> int) raises an exception when passed an odd value, and return an even value when passed an even value.
open Kaputt.Abbreviations let () = check_partial Gen.int f [Spec.is_even_int ==> Spec.is_result Spec.is_even_int ; Spec.is_odd_int ==> Spec.is_exception Spec.always ]
The previous chapter have exposed how to run tests using the Test.run_tests function. When only passed a list of tests, the outcome of these tests is written to the standard output in a (hopefully) user-friendly text setting. It is however possible to change both the destination and the layout by supplying an optional output parameter of type Test.output_mode, that is a sum type with the following constructors:
The passed channel is closed if it is neither stdout, nor stderr.
Test 'succ test' ... 100/100 cases passed Test 'untitled no 1' ... 10/10 cases passed Test 'sum of odds' ... 200/200 cases passed Test 'strings' ... 0/2 case passed counterexamples: "eYbHu", "UEggsF" categories: short -> 1 occurrence long -> 1 occurrence Test 'lists' ... 0/2 case passed counterexamples: [ 6; 5; 1; 3; 6; ], [ 3; 2; 6; ]
<kaputt-report> <random-test name="succ test" valid="100" total="100" uncaught="0"> </random-test> <random-test name="untitled no 1" valid="10" total="10" uncaught="0"> </random-test> <random-test name="sum of odds" valid="200" total="200" uncaught="0"> </random-test> <random-test name="strings" valid="0" total="2" uncaught="0"> <counterexamples> <counterexample value=""OAsdUXKf""/> <counterexample value=""dhVMK""/> </counterexamples> <categories> <category name="long" total="1"/> <category name="short" total="1"/> </categories> </random-test> <random-test name="lists" valid="0" total="2" uncaught="0"> <counterexamples> <counterexample value="[ 5; 1; 6; ]"/> <counterexample value="[ 6; 3; ]"/> </counterexamples> </random-test> </kaputt-report>
random-test (stats)|succ test|100|100|0 random-test (stats)|untitled no 1|10|10|0 random-test (stats)|sum of odds|200|200|0 random-test (stats)|strings|0|2|0 random-test (counterexamples)|strings|"SHwJpJ"|"tbMlVNwqh" random-test (stats)|lists|0|2|0 random-test (counterexamples)|lists|[ 3; 6; 6; ]|[ 3; 4; 5; ]
<!ELEMENT kaputt-report (passed-test|failed-test|uncaught-exception|random-test|enum-test|shell-test)*> <!ELEMENT passed-test EMPTY> <!ATTLIST passed-test name CDATA #REQUIRED> <!ELEMENT failed-test EMPTY> <!ATTLIST failed-test name CDATA #REQUIRED> <!ATTLIST failed-test expected CDATA> <!ATTLIST failed-test not-expected CDATA> <!ATTLIST failed-test actual CDATA #REQUIRED> <!ATTLIST failed-test message CDATA> <!ELEMENT uncaught-exception EMPTY> <!ATTLIST uncaught-exception name CDATA #REQUIRED> <!ATTLIST uncaught-exception exception CDATA #REQUIRED> <!ELEMENT random-test (counterexamples?,categories?)> <!ATTLIST random-test name CDATA #REQUIRED> <!ATTLIST random-test valid CDATA #REQUIRED> <!ATTLIST random-test total CDATA #REQUIRED> <!ATTLIST random-test uncaught CDATA #REQUIRED> <!ELEMENT enum-test (counterexamples?)> <!ATTLIST enum-test name CDATA #REQUIRED> <!ATTLIST enum-test valid CDATA #REQUIRED> <!ATTLIST enum-test total CDATA #REQUIRED> <!ATTLIST enum-test uncaught CDATA #REQUIRED> <!ELEMENT counterexamples (counterexample*)> <!ELEMENT counterexample EMPTY> <!ATTLIST counterexample value CDATA #REQUIRED> <!ELEMENT categories (category*)> <!ELEMENT category EMPTY> <!ATTLIST category name CDATA #REQUIRED> <!ATTLIST category total CDATA #REQUIRED> <!ELEMENT shell-test EMPTY> <!ATTLIST shell-test name CDATA #REQUIRED> <!ATTLIST shell-test exit-code CDATA #REQUIRED>
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