Dear list, during many years of Java programming I've been faithful to TDD methology. Recently I've been trying to figure out how to do tests in Haskell. Thanks to RWH and help from great folks at #haskell I've managed to get on my feet. There is however one issue I wasn't able to solve. In Java it is very easy to separate test code from the actual source. A Java project simply contains two folders: src and tests. These two are treated as the source directories. Both these directories have the same subdirectory structure. For example I have a source file src/myPackage/mySubpackage/MyClass.java and test for it are kept in file tests/myPackage/mySubpackage/MyClassTest.java. These two files are considered by Java to be in the same package. Here's the main trick: fileds and methods that are marked as protected in Java are accessible to other classes in the same package. This allows to test internal methods of a class by marking them as protected instead of private. This breaks encapsulation but only within a package, which is acceptable. Now I'd like to achieve something similar in Haskell. I'm using cabal's support for testing. I created separate src and tests directories, both with the same subdirectory structure. I keep tests for each module in a separate file (e.g. I have src/Math/MyModule.hs and tests/Math/MyModuleTest.hs) and I have one file that assembles all the tests into a single test suite (I use test-framework for that). The only problem is that in order to test some function from a module I have to expose that function, which pretty much forces me to give up on encapsulation. Is there any better solution to organize tests in Haskell? Should I just give up on module encapsulation, or should I only test functions exposed by the module and don't worry about internal functions? Perhaps I should use some different approach? Jan
Hi,
Is there any better solution to organize tests in Haskell?
(Disclaimer: I'm the maintainer of Hspec ;) If you use Hspec[1] for testing, you do not have to assemble your individual tests manually into a test suit; hspec-discover[2] takes care of that. There is no comprehensive user's guide for Hspec yet, but a basic introduction is at [3]. If you have any questions, feel free to join in at #hspec on freenode.
Should I just give up on module encapsulation, or should I only test functions exposed by the module and don't worry about internal functions?
You can do it with CPP. Say, if you have a module Foo, with functions foo, bar and baz, where baz is not part of the public interface, then the export list becomes: {-# LANGUAGE CPP #-} module Foo where ( foo , bar #ifdef TEST , baz #endif ) You then run tests with -DTEST. To make development easier you can add a .ghci file to your project, with: echo ':set -DTEST -isrc -itest' > .ghci And of course you need to add cpp-options: -DTEST to your Cabal test-suite section. Cheers, Simon [1] http://hackage.haskell.org/package/hspec [2] https://github.com/hspec/hspec/tree/master/hspec-discover#automatically-disc... [3] http://hspec.github.com/
On 23 Sep 2012, at 10:25, Jan Stolarek wrote:
Dear list,
during many years of Java programming I've been faithful to TDD methology. Recently I've been trying to figure out how to do tests in Haskell. Thanks to RWH and help from great folks at #haskell I've managed to get on my feet. There is however one issue I wasn't able to solve.
In Java it is very easy to separate test code from the actual source. A Java project simply contains two folders: src and tests. These two are treated as the source directories. Both these directories have the same subdirectory structure. For example I have a source file src/myPackage/mySubpackage/MyClass.java and test for it are kept in file tests/myPackage/mySubpackage/MyClassTest.java. These two files are considered by Java to be in the same package. Here's the main trick: fileds and methods that are marked as protected in Java are accessible to other classes in the same package. This allows to test internal methods of a class by marking them as protected instead of private. This breaks encapsulation but only within a package, which is acceptable.
Now I'd like to achieve something similar in Haskell. I'm using cabal's support for testing. I created separate src and tests directories, both with the same subdirectory structure. I keep tests for each module in a separate file (e.g. I have src/Math/MyModule.hs and tests/Math/MyModuleTest.hs) and I have one file that assembles all the tests into a single test suite (I use test-framework for that). The only problem is that in order to test some function from a module I have to expose that function, which pretty much forces me to give up on encapsulation.
Is there any better solution to organize tests in Haskell? Should I just give up on module encapsulation, or should I only test functions exposed by the module and don't worry about internal functions? Perhaps I should use some different approach?
Jan
Hi, From looking at other packages on Hackage a common trick seems to be to create some internal modules, then have an external module that simply exposes the 'public' functions. Your internal tests can then import the internal modules, and your API tests can import the external module. Of course others are still able to import your Internal modules, but you have at least made it clear that that is a bad idea. for example: MyLib/Internal/Lib.hs: module MyLib.Internal.Lib where -- exports all the functions defined in this function internalFunction = ... externalFunction = ... MyLib/Lib.hs module MyLib.Lib ( -- exports only the public functions externalFunction ) where import MyLib.Internal.Lib -- imports all the internal functions test/Internal/Lib.hs ... import MyLib.Internal.Lib ... test/Lib.hs ... import MyLib.Lib -- imports only the public API ... Yesod is an example of a large project using this approach, for example https://github.com/yesodweb/yesod/tree/master/yesod-core Matt
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Of course others are still able to import your Internal modules
That is not necessarily true. For libraries, you can list internal modules as other-modules (in contrast to exposed-modules) in you Cabal file. That way they are not part of the public interface of your library. However, that approach does not work if you want to do encapsulation within a single project. I think in that case you most likely end up with CPP (it's ugly, but it works). Cheers, Simon
Thanks for replies. CPP approach seems to be what I would like to achieve, but it looks more like a hack than a real solution. That said, I like the idea of creating a module that acts as an external interface to the library and I I don't mind sacrificing encapsulation within the package itself. If it works for project as big as Yesod it should work for me.
If you use Hspec[1] for testing, you do not have to assemble your individual tests manually into a test suit; hspec-discover[2] takes care of that. I guess that I like to have my tests organized manually. It takes a bit of more work and there's a risk that I forget to add some test to the suite, but I'm willing to accept these drawbacks and get more fine-grained control in return.
Jan
On Sun, Sep 23, 2012 at 04:10:56PM +0200, Jan Stolarek wrote:
I don't mind sacrificing encapsulation within the package itself. If it works for project as big as Yesod it should work for me.
Yesod uses the CPP solution, too (e.g. [1]). Cheers, Simon [1] https://github.com/yesodweb/shakespeare/blob/master/shakespeare/Text/Shakesp...
Simon Hengel wrote:
Of course others are still able to import your Internal modules
That is not necessarily true. For libraries, you can list internal modules as other-modules (in contrast to exposed-modules) in you Cabal file. That way they are not part of the public interface of your library.
How do I access internal modules with cabal test , though? Last time I tried, I could not find a way to expose in the test section of the cabal file. Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com
On Sun, Sep 23, 2012 at 06:11:59PM +0200, Heinrich Apfelmus wrote:
Simon Hengel wrote:
Of course others are still able to import your Internal modules
That is not necessarily true. For libraries, you can list internal modules as other-modules (in contrast to exposed-modules) in you Cabal file. That way they are not part of the public interface of your library.
How do I access internal modules with cabal test , though? Last time I tried, I could not find a way to expose in the test section of the cabal file.
It works, if you add the source directory to hs-source-dirs of the test suite (in contrast to depending on the library!), e.g.: hs-source-dirs: test, src or hs-source-dirs: test, . This still has the disadvantage, that the sources are compiled twice. But I'm not aware of a better way to do it. If you mostly use GHCi for development, it's not a big issue. Cheers, Simon
Simon Hengel wrote:
On Sun, Sep 23, 2012 at 06:11:59PM +0200, Heinrich Apfelmus wrote:
How do I access internal modules with cabal test , though? Last time I tried, I could not find a way to expose in the test section of the cabal file.
It works, if you add the source directory to hs-source-dirs of the test suite (in contrast to depending on the library!), e.g.:
hs-source-dirs: test, src
or
hs-source-dirs: test, .
This still has the disadvantage, that the sources are compiled twice. But I'm not aware of a better way to do it. If you mostly use GHCi for development, it's not a big issue.
I got it to work, thanks! I also had to duplicate the dependency information, but that's alright. Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com
participants (4)
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Heinrich Apfelmus -
Jan Stolarek -
Matthew West -
Simon Hengel