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Re: [jfw] Private methods should not be unit-tested
I understand the arguments. I personally would encourage writing tests
for private methods for a good number of reasons (not least of which
is isolating "which" private method is breaking), but I can see the
argument that the "code coverage" figure could exclude private
methods. I wouldn't support deleting the tests (in a company situation
where you have stable development teams, I might be persuaded, but not
in our situation).
On 15 March 2014 07:38, Herman Peeren <herman.peeren AT gmail.com> wrote:
> Private methods should not be unit-tested. Code quality would improve if we
> delete those tests.
> It sounds weird and I understand it is felt as a waste to delete work you've
> done and lowering the code coverage, but I'll explain. Testing is not an
> improvement of code robustness in itself. It is done to test if the results
> are the same when you change the code. Change is the only constant in
> software development, that is why testing is important. Testing should
> therefore be done to an interface, not to an implementation. If you test an
> implementation, you are making the code more rigid, less flexible: for an
> other implementation could be an improvement of the code. Testing the
> implementation prevents change. Private methods are only necessary as part
> of the implementation.
> In a way we have made ourselves prisoners of the "code coverage"
> measurement. It is easy: we just look at a number and are more satisfied if
> it is in the direction of 100% and sad if it is in the direction of zero.
> Colors in the tools we use support that: the more 100% = the more green =
> good and happy. Zero = red = wrong. The tools and measurements get a life on
> their own. We almost forget that the tools there are to help us, not the
> other way around.
> I mainly came to this conclusion after watching "The Magic Tricks of
> Testing" presentation by Ruby star Sandi Metz; see for instance
> https://www.youtube.com/watch?v=qPfQM4w4I04 and
> She points out that we should only have assertions for incoming queries and
> commands, asserting the result of an incoming query and the direct public
> side effects of an incoming command. For the outgoing commands we should
> only test the expectation that they are sent. We should ignore all tests of
> messages sent to self (they test the implementation , not the interface) and
> outgoing query messages (they are redundant). Testing private methods can be
> usefull during development (certainly if you follow a TDD road), but should
> be deleted afterwards. Or, funny moment in Sandi's presentation: be marked
> as "delete these tests if they fail".
> Some other arguments against testing too much can be found in a recent paper
> by James Coplien ('Cope') "Why Most Unit Testing is Waste" :
> During the coming GSOC (Google Summer of Code) several students apply to
> work on more Unit Tests for Joomla. The main measurement for success is
> "code coverage". I hope we will get some better criteria in. Maybe we can
> even improve some code by having less testing code.
> I looked for tested private methods in the Joomla Framework and fortunately
> found not much matching that criterium:
> Private methods that are currently tested in the Joomla Framework (only in 4
> The private methods Joomla\Archive\Zip::readZipInfo and
> Joomla\Archive\Zip::getFileData are marked as covered in the test of the
> calling Joomla\Archive\Zip::extractCustom , which could be a way to get more
> This is the other way around, marking the private methods as
> $this->markTestSkipped('This method is tested via requesting classes.');
> In order to preserve our "good feeling" about code coverage, we could adopt
> a standard way of marking private methods as covered. Or just take the code
> coverage as measure with a grain of salt, in favour of better judgement for
> the need and desirability of tests.
> Framework source code: https://github.com/joomla/joomla-framework
> Visit http://developer.joomla.org for more information about developing with
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