mirror of
https://gitlab.torproject.org/tpo/core/tor.git
synced 2024-11-10 21:23:58 +01:00
402 lines
15 KiB
Plaintext
402 lines
15 KiB
Plaintext
|
|
Writing tests for Tor: an incomplete guide
|
|
==========================================
|
|
|
|
Tor uses a variety of testing frameworks and methodologies to try to
|
|
keep from introducing bugs. The major ones are:
|
|
|
|
1. Unit tests written in C and shipped with the Tor distribution.
|
|
|
|
2. Integration tests written in Python and shipped with the Tor
|
|
distribution.
|
|
|
|
3. Integration tests written in Python and shipped with the Stem
|
|
library. Some of these use the Tor controller protocol.
|
|
|
|
4. System tests written in Python and SH, and shipped with the
|
|
Chutney package. These work by running many instances of Tor
|
|
locally, and sending traffic through them.
|
|
|
|
5. The Shadow network simulator.
|
|
|
|
How to run these tests
|
|
----------------------
|
|
|
|
=== The easy version
|
|
|
|
To run all the tests that come bundled with Tor, run "make check"
|
|
|
|
To run the Stem tests as well, fetch stem from the git repository,
|
|
set STEM_SOURCE_DIR to the checkout, and run "make test-stem".
|
|
|
|
To run the Chutney tests as well, fetch chutney from the git repository,
|
|
set CHUTNEY_PATH to the checkout, and run "make test-network".
|
|
|
|
To run all of the above, run "make test-full".
|
|
|
|
To run all of the above, plus tests that require a working connection to the
|
|
internet, run "make test-full-online".
|
|
|
|
=== Running particular subtests
|
|
|
|
The Tor unit tests are divided into separate programs and a couple of
|
|
bundled unit test programs.
|
|
|
|
Separate programs are easy. For example, to run the memwipe tests in
|
|
isolation, you just run ./src/test/test-memwipe .
|
|
|
|
To run tests within the unit test programs, you can specify the name
|
|
of the test. The string ".." can be used as a wildcard at the end of the
|
|
test name. For example, to run all the cell format tests, enter
|
|
"./src/test/test cellfmt/..". To run
|
|
|
|
Many tests that need to mess with global state run in forked subprocesses in
|
|
order to keep from contaminating one another. But when debugging a failing test,
|
|
you might want to run it without forking a subprocess. To do so, use the
|
|
"--no-fork" option with a single test. (If you specify it along with
|
|
multiple tests, they might interfere.)
|
|
|
|
You can turn on logging in the unit tests by passing one of "--debug",
|
|
"--info", "--notice", or "--warn". By default only errors are displayed.
|
|
|
|
Unit tests are divided into "./src/test/test" and "./src/test/test-slow".
|
|
The former are those that should finish in a few seconds; the latter tend to
|
|
take more time, and may include CPU-intensive operations, deliberate delays,
|
|
and stuff like that.
|
|
|
|
=== Finding test coverage
|
|
|
|
Test coverage is a measurement of which lines your tests actually visit.
|
|
|
|
When you configure Tor with the --enable-coverage option, it should
|
|
build with support for coverage in the unit tests, and in a special
|
|
"tor-cov" binary.
|
|
|
|
Then, run the tests you'd like to see coverage from. If you have old
|
|
coverage output, you may need to run "reset-gcov" first.
|
|
|
|
Now you've got a bunch of files scattered around your build directories
|
|
called "*.gcda". In order to extract the coverage output from them, make a
|
|
temporary directory for them and run "./scripts/test/coverage ${TMPDIR}",
|
|
where ${TMPDIR} is the temporary directory you made. This will create a
|
|
".gcov" file for each source file under tests, containing that file's source
|
|
annotated with the number of times the tests hit each line. (You'll need to
|
|
have gcov installed.)
|
|
|
|
You can get a summary of the test coverage for each file by running
|
|
"./scripts/test/cov-display ${TMPDIR}/*" . Each line lists the file's name,
|
|
the number of uncovered lines, the number of uncovered lines, and the
|
|
coverage percentage.
|
|
|
|
For a summary of the test coverage for each _function_, run
|
|
"./scripts/test/cov-display -f ${TMPDIR}/*" .
|
|
|
|
=== Comparing test coverage
|
|
|
|
Sometimes it's useful to compare test coverage for a branch you're writing to
|
|
coverage from another branch (such as git master, for example). But you
|
|
can't run "diff" on the two coverage outputs directly, since the actual
|
|
number of times each line is executed aren't so important, and aren't wholly
|
|
deterministic.
|
|
|
|
Instead, follow the instructions above for each branch, creating a separate
|
|
temporary directory for each. Then, run "./scripts/test/cov-diff ${D1}
|
|
${D2}", where D1 and D2 are the directories you want to compare. This will
|
|
produce a diff of the two directories, with all lines normalized to be either
|
|
covered or uncovered.
|
|
|
|
To count new or modified uncovered lines in D2, you can run:
|
|
|
|
"./scripts/test/cov-diff ${D1} ${D2}" | grep '^+ *\#' |wc -l
|
|
|
|
|
|
What kinds of test should I write?
|
|
----------------------------------
|
|
|
|
Integration testing and unit testing are complementary: it's probably a
|
|
good idea to make sure that your code is hit by both if you can.
|
|
|
|
If your code is very-low level, and its behavior is easily described in
|
|
terms of a relation between inputs and outputs, or a set of state
|
|
transitions, then it's a natural fit for unit tests. (If not, please
|
|
consider refactoring it until most of it _is_ a good fit for unit
|
|
tests!)
|
|
|
|
If your code adds new externally visible functionality to Tor, it would
|
|
be great to have a test for that functionality. That's where
|
|
integration tests more usually come in.
|
|
|
|
Unit and regression tests: Does this function do what it's supposed to?
|
|
-----------------------------------------------------------------------
|
|
|
|
Most of Tor's unit tests are made using the "tinytest" testing framework.
|
|
You can see a guide to using it in the tinytest manual at
|
|
|
|
https://github.com/nmathewson/tinytest/blob/master/tinytest-manual.md
|
|
|
|
To add a new test of this kind, either edit an existing C file in src/test/,
|
|
or create a new C file there. Each test is a single function that must
|
|
be indexed in the table at the end of the file. We use the label "done:" as
|
|
a cleanup point for all test functions.
|
|
|
|
(Make sure you read tinytest-manual.md before proceeding.)
|
|
|
|
I use the term "unit test" and "regression tests" very sloppily here.
|
|
|
|
=== A simple example
|
|
|
|
Here's an example of a test function for a simple function in util.c:
|
|
|
|
static void
|
|
test_util_writepid(void *arg)
|
|
{
|
|
(void) arg;
|
|
|
|
char *contents = NULL;
|
|
const char *fname = get_fname("tmp_pid");
|
|
unsigned long pid;
|
|
char c;
|
|
|
|
write_pidfile(fname);
|
|
|
|
contents = read_file_to_str(fname, 0, NULL);
|
|
tt_assert(contents);
|
|
|
|
int n = sscanf(contents, "%lu\n%c", &pid, &c);
|
|
tt_int_op(n, OP_EQ, 1);
|
|
tt_int_op(pid, OP_EQ, getpid());
|
|
|
|
done:
|
|
tor_free(contents);
|
|
}
|
|
|
|
This should look pretty familiar to you if you've read the tinytest
|
|
manual. One thing to note here is that we use the testing-specific
|
|
function "get_fname" to generate a file with respect to a temporary
|
|
directory that the tests use. You don't need to delete the file;
|
|
it will get removed when the tests are done.
|
|
|
|
Also note our use of OP_EQ instead of == in the tt_int_op() calls.
|
|
We define OP_* macros to use instead of the binary comparison
|
|
operators so that analysis tools can more easily parse our code.
|
|
(Coccinelle really hates to see == used as a macro argument.)
|
|
|
|
Finally, remember that by convention, all *_free() functions that
|
|
Tor defines are defined to accept NULL harmlessly. Thus, you don't
|
|
need to say "if (contents)" in the cleanup block.
|
|
|
|
=== Exposing static functions for testing
|
|
|
|
Sometimes you need to test a function, but you don't want to expose
|
|
it outside its usual module.
|
|
|
|
To support this, Tor's build system compiles a testing version of
|
|
each module, with extra identifiers exposed. If you want to
|
|
declare a function as static but available for testing, use the
|
|
macro "STATIC" instead of "static". Then, make sure there's a
|
|
macro-protected declaration of the function in the module's header.
|
|
|
|
For example, crypto_curve25519.h contains:
|
|
|
|
#ifdef CRYPTO_CURVE25519_PRIVATE
|
|
STATIC int curve25519_impl(uint8_t *output, const uint8_t *secret,
|
|
const uint8_t *basepoint);
|
|
#endif
|
|
|
|
The crypto_curve25519.c file and the test_crypto.c file both define
|
|
CRYPTO_CURVE25519_PRIVATE, so they can see this declaration.
|
|
|
|
=== Mock functions for testing in isolation
|
|
|
|
Often we want to test that a function works right, but the function to
|
|
be tested depends on other functions whose behavior is hard to observe,
|
|
or which require a working Tor network, or something like that.
|
|
|
|
To write tests for this case, you can replace the underlying functions
|
|
with testing stubs while your unit test is running. You need to declare
|
|
the underlying function as 'mockable', as follows:
|
|
|
|
MOCK_DECL(returntype, functionname, (argument list));
|
|
|
|
and then later implement it as:
|
|
|
|
MOCK_IMPL(returntype, functionname, (argument list))
|
|
{
|
|
/* implementation here */
|
|
}
|
|
|
|
For example, if you had a 'connect to remote server' function, you could
|
|
declare it as:
|
|
|
|
|
|
MOCK_DECL(int, connect_to_remote, (const char *name, status_t *status));
|
|
|
|
When you declare a function this way, it will be declared as normal in
|
|
regular builds, but when the module is built for testing, it is declared
|
|
as a function pointer initialized to the actual implementation.
|
|
|
|
In your tests, if you want to override the function with a temporary
|
|
replacement, you say:
|
|
|
|
MOCK(functionname, replacement_function_name);
|
|
|
|
And later, you can restore the original function with:
|
|
|
|
UNMOCK(functionname);
|
|
|
|
For more information, see the definitions of this mocking logic in
|
|
testsupport.h.
|
|
|
|
=== Okay but what should my tests actually do?
|
|
|
|
We talk above about "test coverage" -- making sure that your tests visit
|
|
every line of code, or every branch of code. But visiting the code isn't
|
|
enough: we want to verify that it's correct.
|
|
|
|
So when writing tests, try to make tests that should pass with any correct
|
|
implementation of the code, and that should fail if the code doesn't do what
|
|
it's supposed to do.
|
|
|
|
You can write "black-box" tests or "glass-box" tests. A black-box test is
|
|
one that you write without looking at the structure of the function. A
|
|
glass-box one is one you implement while looking at how the function is
|
|
implemented.
|
|
|
|
In either case, make sure to consider common cases *and* edge cases; success
|
|
cases and failure csaes.
|
|
|
|
For example, consider testing this function:
|
|
|
|
/** Remove all elements E from sl such that E==element. Preserve
|
|
* the order of any elements before E, but elements after E can be
|
|
* rearranged.
|
|
*/
|
|
void smartlist_remove(smartlist_t *sl, const void *element);
|
|
|
|
In order to test it well, you should write tests for at least all of the
|
|
following cases. (These would be black-box tests, since we're only looking
|
|
at the declared behavior for the function:
|
|
|
|
* Remove an element that is in the smartlist.
|
|
* Remove an element that is not in the smartlist.
|
|
* Remove an element that appears in the smartlist more than once.
|
|
|
|
And your tests should verify that it behaves correct. At minimum, you should
|
|
test:
|
|
|
|
* That other elements before E are in the same order after you call the
|
|
functions.
|
|
* That the target element is really removed.
|
|
* That _only_ the target element is removed.
|
|
|
|
When you consider edge cases, you might try:
|
|
|
|
* Remove an element from an empty list.
|
|
* Remove an element from a singleton list containing that element.
|
|
* Remove an element for a list containing several instances of that
|
|
element, and nothing else.
|
|
|
|
Now let's look at the implementation:
|
|
|
|
void
|
|
smartlist_remove(smartlist_t *sl, const void *element)
|
|
{
|
|
int i;
|
|
if (element == NULL)
|
|
return;
|
|
for (i=0; i < sl->num_used; i++)
|
|
if (sl->list[i] == element) {
|
|
sl->list[i] = sl->list[--sl->num_used]; /* swap with the end */
|
|
i--; /* so we process the new i'th element */
|
|
sl->list[sl->num_used] = NULL;
|
|
}
|
|
}
|
|
|
|
Based on the implementation, we now see three more edge cases to test:
|
|
|
|
* Removing NULL from the list.
|
|
* Removing an element from the end of the list
|
|
* Removing an element from a position other than the end of the list.
|
|
|
|
|
|
=== What should my tests NOT do?
|
|
|
|
Tests shouldn't require a network connection.
|
|
|
|
Whenever possible, tests shouldn't take more than a second. Put the test
|
|
into test/slow if it genuinely needs to be run.
|
|
|
|
Tests should not alter global state unless they run with TT_FORK: Tests
|
|
should not require other tests to be run before or after them.
|
|
|
|
Tests should not leak memory or other resources.
|
|
|
|
When possible, tests should not be over-fit to the implementation. That is,
|
|
the test should verify that the documented behavior is implemented, but
|
|
should not break if other permissible behavior is later implemented.
|
|
|
|
|
|
=== Advanced techniques: Namespaces
|
|
|
|
Sometimes, when you're doing a lot of mocking at once, it's convenient to
|
|
isolate your identifiers within a single namespace. If this were C++, we'd
|
|
already have namespaces, but for C, we do the best we can with macros and
|
|
token-pasting.
|
|
|
|
We have some macros defined for this purpose in src/test/test.h. To use
|
|
them, you define NS_MODULE to a prefix to be used for your identifiers, and
|
|
then use other macros in place of identifier names. See src/test/test.h for
|
|
more documentation.
|
|
|
|
|
|
Integration tests: Calling Tor from the outside
|
|
-----------------------------------------------
|
|
|
|
Some tests need to invoke Tor from the outside, and shouldn't run from the
|
|
same process as the Tor test program. Reasons for doing this might include:
|
|
|
|
* Testing the actual behavior of Tor when run from the command line
|
|
* Testing that a crash-handler correctly logs a stack trace
|
|
* Verifying that a violating a sandbox or capability requirement will
|
|
actually crash the program.
|
|
* Needing to run as root in order to test capability inheritance or
|
|
user switching.
|
|
|
|
To add one of these, you generally want a new C program in src/test. Add it
|
|
to TESTS and noinst_PROGRAMS if it can run on its own and return success or
|
|
failure. If it needs to be invoked multiple times, or it needs to be
|
|
wrapped, add a new shell script to TESTS, and the new program to
|
|
noinst_PROGRAMS. If you need access to any environment variable from the
|
|
makefile (eg ${PYTHON} for a python interpreter), then make sure that the
|
|
makefile exports them.
|
|
|
|
Writing integration tests with Stem
|
|
-----------------------------------
|
|
|
|
The 'stem' library includes extensive unit tests for the Tor controller
|
|
protocol.
|
|
|
|
For more information on writing new tests for stem, have a look around
|
|
the tst/* directory in stem, and find a good example to emulate. You
|
|
might want to start with
|
|
https://gitweb.torproject.org/stem.git/tree/test/integ/control/controller.py
|
|
to improve Tor's test coverage.
|
|
|
|
You can run stem tests from tor with "make test-stem", or see
|
|
https://stem.torproject.org/faq.html#how-do-i-run-the-tests .
|
|
|
|
System testing with Chutney
|
|
---------------------------
|
|
|
|
The 'chutney' program configures and launches a set of Tor relays,
|
|
authorities, and clients on your local host. It has a 'test network'
|
|
functionality to send traffic through them and verify that the traffic
|
|
arrives correctly.
|
|
|
|
You can write new test networks by adding them to 'networks'. To add
|
|
them to Tor's tests, add them to the test-network or test-network-all
|
|
targets in Makefile.am.
|
|
|
|
(Adding new kinds of program to chutney will still require hacking the
|
|
code.)
|