Safe Haskell | None |
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This module provides a short tutorial on how to use the HTF. It assumes that you are using GHC for compiling your Haskell code. (It is possible to use the HTF with other Haskell environments, only the steps taken to invoke the custom preprocessor of the HTF may differ in this case.)
We start with a simple example. Then we show how to use HTF to easily
collect test definitions from multiple modules and discuss
backwards-compatibility for projects already using HUnit
. Finally,
we give a brief cookbook-like summary on how to setup your tests with HTF.
A simple example
Suppose you are trying to write a function for reversing lists :
myReverse :: [a] -> [a] myReverse [] = [] myReverse [x] = [x] myReverse (x:xs) = myReverse xs
To test this function using the HTF, you would first create a new source
file with a OPTIONS_GHC
pragma in the first line.
{-# OPTIONS_GHC -F -pgmF htfpp #-}
This pragma instructs GHC to run the source file through htfpp
, the
custom preprocessor of the HTF.
The following import
statements are also needed:
import System.Environment ( getArgs ) import System.Exit ( exitWith ) import Test.Framework
The actual unit tests and QuickCheck properties are defined like this:
test_nonEmpty = do assertEqual [1] (myReverse [1]) assertEqual [3,2,1] (myReverse [1,2,3]) test_empty = assertEqual ([] :: [Int]) (myReverse []) prop_reverse :: [Int] -> Bool prop_reverse xs = xs == (myReverse (myReverse xs))
When htfpp
consumes the source file, it replaces the assertEqual
tokens (and other assert
-like tokens, see
Test.Framework.HUnitWrapper) with calls to
assertEqual_
, passing
the current location in the file as the first argument.
Moreover, the
preprocessor collects all top-level definitions starting with test_
or prop_
in a test suite of type TestSuite
and name htf_
M_thisModulesTests
,
where M is the name of the current module with dots .
replaced by underscores _
.
For your convenience, the preprocessor also defines the token htf_thisModulesTests
as a shorthand for the rather lengthy name htf_
M_thisModulesTests
.
Definitions starting with test_
denote unit tests and must be of type Assertion
.
Definitions starting with prop_
denote QuickCheck properties and must be of type T such that
T is an instance of the type class Testable
.
To run the tests, use the htfMain
function.
main = htfMain htf_thisModulesTests
Here is the skeleton of a .cabal
file which you may want to use to
compile the tests.
Name: HTF-tutorial Version: 0.1 Cabal-Version: >= 1.10 Build-type: Simple Executable tutorial Type: exitcode-stdio-1.0 Main-is: Tutorial.hs Build-depends: base == 4.*, HTF == 0.10.* Default-language: Haskell2010
Compiling the program just shown (you must include the code for
myReverse
as well), and then running the resulting program with no
further commandline arguments yields the following output (colors had to
be omitted, so the diff output does not look very useful):
[TEST] Main:nonEmpty (Tutorial.hs:17) assertEqual failed at Tutorial.hs:18 * expected: [3, 2, 1] * but got: [3] * diff: [3, 2, 1] *** Failed! (0ms) [TEST] Main:empty (Tutorial.hs:19) +++ OK (0ms) [TEST] Main:reverse (Tutorial.hs:22) Falsifiable (after 6 tests and 5 shrinks): [0,0] Replay argument: "Just (200055706 2147483393,5)" *** Failed! (0ms) [TEST] Main:reverseReplay (Tutorial.hs:24) Falsifiable (after 1 test and 2 shrinks): [0,0] Replay argument: "Just (1060394807 2147483396,2)" *** Failed! (0ms) * Tests: 4 * Passed: 1 * Pending: 0 * Failures: 3 * Errors: 0 * Failures: * Main:reverseReplay (Tutorial.hs:24) * Main:reverse (Tutorial.hs:22) * Main:nonEmpty (Tutorial.hs:17) Total execution time: 4ms
(To check only specific tests, you can pass commandline arguments to the program: the HTF then runs only those tests whose name contain at least one of the commandline arguments as a substring.)
You see that the message for the first failure contains exact location information, which is quite convenient. Also, HTF provides a diff between the expected and the given output. (For this simple example, a diff is kind of useless, but with longer output strings, a diff allows you to identify very quickly where the expected and the given results disagree.)
For the QuickCheck property Main.reverse
, the HTF outputs a string
represenation of the random generator used to check the property. This
string representation can be used to replay the property. (The replay
feature may not be useful for this simple example but it helps in more
complex scenarios).
To replay a property you simply use the string representation of the generator to define a new QuickCheck property with custom arguments:
prop_reverseReplay =withQCArgs
(\a -> a {replay
=read
"Just (1060394807 2147483396,2)" }) prop_reverse
To finish this simple example, we now give a correct definition for myReverse
:
myReverse :: [a] -> [a] myReverse [] = [] myReverse (x:xs) = myReverse xs ++ [x]
Running our tests again on the fixed definition then yields the desired result:
[TEST] Main:nonEmpty (Tutorial.hs:17) +++ OK (0ms) [TEST] Main:empty (Tutorial.hs:19) +++ OK (0ms) [TEST] Main:reverse (Tutorial.hs:22) Passed 100 tests. +++ OK (20ms) [TEST] Main:reverseReplay (Tutorial.hs:24) Passed 100 tests. +++ OK (4ms) * Tests: 4 * Passed: 4 * Pending: 0 * Failures: 0 * Errors: 0 Total execution time: 28ms
The HTF also allows the definition of black box tests. Essentially, black box tests allow you to verify that the output of your program matches your expectations. See the documentation of the Test.Framework.BlackBoxTest module for further information.
Test definitions in multiple modules
For testing real-world programs or libraries, it is often conventient to
split the tests into several modules. For example, suppose your library contains
of two modules MyPkg.A
and MyPkg.B
, each containing test functions.
You can find a slightly extended of this scenario in the samples directory
of the HTF source tree, see https://github.com/skogsbaer/HTF/tree/master/sample.)
File MyPkg/A.hs
{-# OPTIONS_GHC -F -pgmF htfpp #-} module MyPkg.A (funA, htf_thisModulesTests) where import Test.Framework funA :: Int -> Int funA x = x + 1 test_funA1 = assertEqual (funA 41) 42 test_funA2 = assertEqual (funA 2) 3
File MyPkg/B.hs
{-# OPTIONS_GHC -F -pgmF htfpp #-} module MyPkg.B (funB, htf_thisModulesTests) where import Test.Framework funB :: Int -> Int funB x = x * 2 test_funB1 = assertEqual (funB 21) 42 test_funB2 = assertEqual (funB 0) 0
For module MyPkg.A
, the htfpp
preprocessor collects the modules'
testcases into a variable htf_MyPkg_A_thisModulesTests
and defines a
preprocessor token thisModulesTests
as a shorthand for this variable.
Thus, to expose all HTF tests defined in MyPkg.A
, we only
need to put thisModulesTests
into the export list. The same holds
analogously for module MyPkg.B
.
To execute all tests defined in these two modules, you would create
a main module and import MyPkg.A
and MyPkg.B
with the special
import annotation {-@ HTF_TESTS @-}
. The effect of this annotation
is that the htfpp
preprocessor makes all test cases defined in
such modules imported
available in a variable called htf_importedTests
. Thus, your
main module would look like this:
File TestMain.hs
{-# OPTIONS_GHC -F -pgmF htfpp #-} module Main where import Test.Framework import Test.Framework.BlackBoxTest import {-@ HTF_TESTS @-} MyPkg.A import {-@ HTF_TESTS @-} MyPkg.B main = htfMain htf_importedTests
Machine-readable output
For better integration with your testing environment, HTF provides the ability to produce machine-readable output in JSON format. Here is a short example how the JSON output looks like, for details see Test.Framework.JsonOutput:
{"test":{"flatName":"Main:nonEmpty","location":{"file":"Tutorial.hs","line":17},"path":["Main","nonEmpty"],"sort":"unit-test"},"type":"test-start"} ;; {"result":"pass","message":"","test":{"flatName":"Main:nonEmpty","location":{"file":"Tutorial.hs","line":17},"path":["Main","nonEmpty"],"sort":"unit-test"},"wallTime":0,"type":"test-end","location":null} ;; {"test":{"flatName":"Main:empty","location":{"file":"Tutorial.hs","line":19},"path":["Main","empty"],"sort":"unit-test"},"type":"test-start"} ;; {"result":"pass","message":"","test":{"flatName":"Main:empty","location":{"file":"Tutorial.hs","line":19},"path":["Main","empty"],"sort":"unit-test"},"wallTime":0,"type":"test-end","location":null} ;; {"test":{"flatName":"Main:reverse","location":{"file":"Tutorial.hs","line":22},"path":["Main","reverse"],"sort":"quickcheck-property"},"type":"test-start"} ;; {"result":"pass","message":"Passed 100 tests.","test":{"flatName":"Main:reverse","location":{"file":"Tutorial.hs","line":22},"path":["Main","reverse"],"sort":"quickcheck-property"},"wallTime":19,"type":"test-end","location":null} ;; {"test":{"flatName":"Main:reverseReplay","location":{"file":"Tutorial.hs","line":24},"path":["Main","reverseReplay"],"sort":"quickcheck-property"},"type":"test-start"} ;; {"result":"pass","message":"Passed 100 tests.","test":{"flatName":"Main:reverseReplay","location":{"file":"Tutorial.hs","line":24},"path":["Main","reverseReplay"],"sort":"quickcheck-property"},"wallTime":4,"type":"test-end","location":null} ;; {"failures":0,"passed":4,"pending":0,"wallTime":39,"errors":0,"type":"test-results"} ;;
Machine-readable ouput is requested by the --json
flag. You can specify a dedicated output file
using the --output-file=
option. On some platforms (e.g. Windows) it might not be possible to read
from the output file while the tests are running (due to file-locking). In this case, you might want
to use the --split
option. With this option, HTF writes each JSON message to a separate ouput file.
The name of the output file is derived from the name given with the --output-file=
flag by
appending an index (starting at 0) that is incremented for every message.
Backwards-compatibility with HUnit
The types of the various assert
-like macros of the HTF are not backwards-compatible
with the corresponding functions of HUnit. This incompatibility is intentional, of course:
with HUnit, the programmer has to provide suitable location information by explicitly
passing a string argument to the assert
-like functions, whereas HTF provides
location information implicitly through its pre-processor htfpp
.
To simplify transition from HUnit to HTF, htfpp
provides a commandline flag
--hunit
. This flag causes htfpp
to exand the assertion macros in a way compatible
with the types of the corresponding HUnit functions. For example, with the --hunit
flag being present, assertEqual
is exanded to
, whose type
assertEqualVerbose_
(makeLoc
"filename" line)(Show a, Eq a) => String -> a -> a -> IO ()
is compatible with
the type of HUnit's assertEqual
function.
Summary
Here is a quick summary of how to write, collect, and execute your tests. You should also have a look at the sample project at https://github.com/skogsbaer/HTF/tree/master/sample.
Writing tests
- Place
{-# OPTIONS_GHC -F -pgmF htfpp #-}
at the top of your module. - Put
htf_thisModulesTests
into the export list of your module. - Import
Test.Framework
. - Prefix your unit tests with
test_
, see Test.Framework.HUnitWrapper for the assertions provided. - Prefix your QuickCheck properties with
prop_
.
Collecting and executing tests
- Place
{-# OPTIONS_GHC -F -pgmF htfpp #-}
at the top of your module. - Import
Test.Framework
. - Import modules defining HTF tests with
import {-@ HTF_TESTS @-} MyPkg.A
. - Use
main = htfMain htf_importedTests
to run all imported tests.