Leo Simons wrote:
On Wed, Mar 22, 2006 at 08:02:44AM -0500, Geir Magnusson Jr wrote:
Leo Simons wrote:
On Wed, Mar 22, 2006 at 07:15:28AM -0500, Geir Magnusson Jr wrote:
Pulling out of the various threads where we have been discussing, can we
agree on the problem :
We have unique problems compared to other Java projects because we need
to find a way to reliably test the things that are commonly expected to
be a solid point of reference - namely the core class library.
Further, we've been implicitly doing "integration testing" because - so
far - the only way we've been testing our code has been 'in situ' in the
VM - not in an isolated test harness. To me, this turns it into an
integration test.
Sure, we're using JUnit, but because of the fact we are implmenting core
java.* APIs, we aren't testing with a framework that has been
independently tested for correctness, like we would when testing any
other code.
I hope I got that idea across - I believe that we have to go beyond
normal testing approaches because we don't have a normal situation.
Where we define 'normal situation' as "running a test framework on top of
the sun jdk and expecting any bugs to not be in that jdk". There's plenty
of projects out there that have to test things without having such a
"stable reference JDK" luxury.....I imagine that testing GCC is just as
hard as this problem we have here :-)
Is it the same? We need to have a running JVM+classlibarary to test the
classlibrary code.
Well you need a working C compiler and standard C library to compile the
compiler so you can compile make so you can build bash so you can run
perl (which uses the standard C library functions all over the place of
course) so you can run the standard C library tests so that you know that
the library you used when compiling the compiler were correct so you can
run the compiler tests. I don't think they actually do things that way, but
it seems like basically the same problem. Having a virtual machine just
makes it easier since you still assume "the native world" as a baseline,
which is a lot more than "the hardware".
There's a difference. You can use a completely separate toolchain to
build, test and verify the output of the C compiler.
In our case, we are using the thing we are testing to test itself.
There is no "known good" element possible right now.
We use the classlibrary we are trying to test to execute the test
framework that tests the classlibrary that is running it.
The tool is testing itself.
So I think there are three things we want to do (adopting the
terminology that came from the discussion with Tim and Leo ) :
1) implementation tests
2) spec/API tests (I'll bundle together)
3) integration/functional tests
I believe that for #1, the issues related to being on the bootclasspath
don't matter, because we aren't testing that aspect of the classes
(which is how they behave integrated w/ the VM and security system) but
rather the basic internal functioning.
I'm not sure how to approach this, but I'll try. I'd love to hear how
Sun, IBM or BEA deals with this, or be told why it isn't an issue :)
Implementation tests : I'd like to see us be able to do #1 via the
standard same-package technique (i.e. testing a.b.C w/ a.b.CTest) but
we'll run into a tangle of classloader problems, I suspect, becuase we
want to be testing java.* code in a system that already has java.* code.
Can anyone see a way we can do this - test the classlibrary from the
integration point of view - using some test harness + any known-good
JRE, like Sun's or IBM's?
Ew, that won't work in the end since we should assume our own JRE is going
to be "known-better" :-). But it might be a nice way to "bootstrap" (eg
we test with an external JRE until we satisfy the tests and then we switch
to testing with an earlier build).
Lets be clear - even using our own "earlier build" doesn't solve the
problem I'm describing, because as it stands now, we don't use "earlier
build" classes to test with - we use the code we want to test as the
clsaslibrary for the JRE that's running the test framework.
The classes that we are testing are also the classes used by the testing
framework. IOW, any of the java.* classes that JUnit itself needs (ex.
java.util.HashMap) are exactly the same implementation that it's testing.
That's why I think it's subtly different than a "bootstrap and use
version - 1 to test" problem. See what I mean?
Yeah yeah, I was already way beyond thinking "just" JUnit is usable for the
kind of test you're describing. At some point, fundamentally, you either trust
something external (whether its the sun jdk or the intel compiler designers,
at some point you do draw a line) or you find a way to bootstrap.
Well, we do trust the Sun JDK.
I'm very open to the idea that I'm missing something here, but I'd like
to know that you see the issue - that when we test, we have
VM + "classlib to be tested" + JUnit + testcases
where the testcases are testing the classlib the VM is running JUnit with.
There never is isolation of the code being tested :
VM + "known good classlib" + Junit + testcases
unless we have some framework where
VM + "known good classlib" + JUnit
+ framework("classlib to be tested")
+ testcases
and it's that notion of "framework()" that I'm advocating we explore.
I'm all for exploring it, I just fundamentally don't buy into the "known
good" bit. What happens when the 'classlib to be tested' is 'known
better' than the 'known good' one? How do you define "known"? How do you
define "good"?
Known? Passed some set of tests. So it could be the Sun JDK for the VM
+ "known good" part.
I think you intuitively understand this. When you find a bug in code
you are testing, you first assume it's your code, not the framework,
right? In our case, our framework is actually the code we are testing,
so we have a bit of a logical conundrum.
Further ideas...
-> look at how the native world does testing
(hint: it usually has #ifdefs, uses perl along the way, and it is
certainly
"messy")
-> emulate that
-> build a bigger, better specification test
-> and somehow "prove" it is "good enough"
-> build a bigger, better integration test
-> and somehow "prove" it is "good enough"
I'll admit my primary interest is the last one...
The problem I see with the last one is that the "parameter space" is *huge*.
Yeah, that's one of the things that makes it interesting. Fortunately
open source does have many monkeys...
I believe that your preference for the last one comes from the
Monte-Carlo style approach that Gump uses - hope that your test suite
has enough variance that you "push" the thing being tested through
enough of the parameter space that you can be comfortable you would have
exposed the bugs. Maybe.
Ooh, now its becoming rather abstract...
Well, perhaps, but more of the gump approache comes from the idea that
the parameter space itself is also at some point defined in software,
which may have bugs of its own. You circumvent that by making humans the
parameter space (don't start about how humans are buggy. We don't want to
get into existialism or faith systems when talking about unit testing do
we?). The thing that gump enables is "many monkey QA" - a way for thousands
of human beings to concurrently make shared assertions about software
without actually needing all that much human interaction.
More concretely, if harmony can run all known java software, and run it to
the asserted satisfaction of all its developers, you can trust that you have
covered all the /relevant/ parts of the parameter space you describe.
Yes. And when you can run all knownn Java software, let me know :)
That's my point about the parameter space being huge. Even when you
reduce the definition to "that of all known Java software", you still
have a huge problem on your hands.
You
will never get that level of trust when the assertions are made by software
rather than humans. This is how open source leads to software quality.
Quoting myself, 'gump is the most misunderstood piece of software, ever'.
cheers,
Leo
