On 01/05/2011 06:12 PM, Avi Kivity wrote:
On 01/05/2011 05:45 PM, Michael Goldish wrote:
In complex tests (KVM) an exception string is often not informative
enough and
the traceback and source code have to be examined in order to figure
out what
caused the exception. Context strings are a way for tests to provide
information about what they're doing, so that when an exception is
raised, this
information will be embedded in the exception string. The result is
a concise
yet highly informative exception string, which should make it very
easy to
figure out where/when the exception was raised.
A typical example for a test where this may be useful is KVM's reboot
test.
Some exceptions can be raised either before or after the VM is
rebooted (e.g.
logging into the guest can fail) and whether they are raised before
or after
is critical to the understanding of the failure. Normally the
traceback would
have to be examined, but the proposed method makes it easy to know
where the
exception is raised without doing so. To achieve this, the reboot
test should
place calls to error.context() as follows:
error.context("before reboot")
<carry out pre-reboot actions>
error.context("sending reboot command")
<send the reboot command>
error.context("after reboot")
<carry out post-reboot actions>
If login fails in the pre-reboot section, the resulting exception
string can
can have something like "context: before reboot" embedded in it.
(The actual
embedding is done in the next patch in the series.)
It would be nice to make the error context a stack, and to use the
with statement to manage the stack:
with error.context("main test"):
foo()
with error.context("before reboot"):
bar()
If foo() throws an exception, the context would be "main test", while
if bar() throws an exception, the context would be "before reboot" in
"main test".
btw, you can have a decorator for enclosing an entire function in an
error context:
@function_error_context('migration test')
def migration_test(...):
...
anything in migration_test() is enclosed in that context. But we're
just repeating the ordinary stack trace with something more readable.
--
error compiling committee.c: too many arguments to function
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