If you just want to write a simple test case, check out the file
writing_tests.md.
This test suite is intended for system tests, i.e. for running a binary with certain parameters and comparing the output against an expected value. This is especially useful for a regression test suite, but can be also used for testing of new features where unit testing is not feasible, e.g. to test new command line parameters.
The test suite is configured via INI style files using Python's builtin
ConfigParser
module. Such a configuration file looks roughly like this:
[DEFAULT] some_var: some_val [section 1] empty_var: multiline_var: this is a multiline string as long as the indentation is present # comments can be inserted # some_var is implicitly present in this section by the DEFAULT section [section 2] # set some_var for this section to something else than the default some_var: some_other_val # values from other sections can be inserted vars can have whitespaces: ${some_var} ${section 1: multiline var} multiline var: multiline variables can have empty lines too
For further details concerning the syntax, please consult the official
documentation. The ConfigParser module is used with the following defaults:
- Comments are started by # only
- The separator between a variable and the value is :
- Multiline comments can have empty lines
- Extended Interpolation is used (this allows to refer to other sections when
inserting values using the ${section:variable} syntax)
Please keep in mind that leading and trailing whitespaces are stripped from strings when extracting variable values. So this:
some_var: some value with whitespaces before and after
is equivalent to this:
some_var:some value with whitespaces before and after
The test suite itself uses the builtin unittest module of Python to discover
and run the individual test cases. The test cases themselves are implemented in
Python source files, but the required Python knowledge is minimal.
The test suite is configured via one configuration file whose location
automatically sets the root directory of the test suite. The unittest module
then recursively searches all sub-directories with a __init__.py file for
files of the form test_*.py, which it automatically interprets as test cases
(more about these in the next section). Python will automatically interpret each
directory as a module and use this to format the output, e.g. the test case
regression/crashes/test_bug_15.py will be interpreted as the module
regression.crashes.test_bug_15. Thus one can use the directory structure to
group test cases.
The test suite's configuration file should have the following form:
[General] timeout: 0.1 [paths] binary: ../build/bin/binary important_file: ../conf/main.cfg [variables] abort_error: ERROR abort_exit value: 1
The General section only contains the timeout parameter, which is actually
optional (when left out 1.0 is assumed). The timeout sets the maximum time in
seconds for each command that is run before it is aborted. This allows for test
driven development with tests that cause infinite loops or similar hangs in the
test suite.
The paths and variables sections define global variables for the system test suite, which every test case can read. Following the DRY principle, one can put common outputs of the tested binary in a variable, so that changing an error message does not result in an hour long update of the test suite. Both sections are merged together before being passed on to the test cases, thus they must not contain variables with the same name (doing so results in an error).
While the values in the variables section are simply passed on to the test cases the paths section is special as its contents are interpreted as relative paths (with respect to the test suite's root) and are expanded to absolute paths before being passed to the test cases. This can be used to inform each test case about the location of a built binary or a configuration file without having to rely on environment variables.
However, sometimes environment variables are very handy to implement variable
paths or platform differences (like different build directories or file
extensions). For this, the test suite supports the ENV and ENV fallback
sections. In conjunction with the extended interpolation of the ConfigParser
module, these can be quite useful. Consider the following example:
[General] timeout: 0.1 [ENV] variable_prefix: PREFIX file_extension: FILE_EXT [ENV fallback] variable_prefix: ../build [paths] binary: ${ENV:variable_prefix}/bin/binary${ENV:file_extension} important_file: ../conf/main.cfg [variables] abort_error: ERROR abort_exit value: 1
The ENV section is, similarly to the paths section, special insofar as the
variables are extracted from the environment with the given name. E.g. the
variable file_extension would be set to the value of the environment variable
FILE_EXT. If the environment variable is not defined, then the test suite will
look in the ENV fallback section for a fallback. E.g. in the above example
variable_prefix has the fallback or default value of ../build which will be
used if the environment variable PREFIX is not set. If no fallback is provided
then an empty string is used instead, which would happen to file_extension if
FILE_EXT would be unset.
This can be combined with the extended interpolation of Python's ConfigParser,
which allows to include variables from arbitrary sections into other variables
using the ${sect:var_name} syntax. This would be expanded to the value of
var_name from the section sect. The above example only utilizes this in the
paths section, but it can also be used in the variables section, if that
makes sense for the use case.
Returning to the example config file, the path binary would be inferred in the
following steps:
1. extract PREFIX & FILE_EXT from the environment, if they don't exist use
the default values from ENV fallback or ""
2. substitute the strings ${ENV:variable_prefix} and ${ENV:file_extension}
3. expand the relative path to an absolute path
Please note that while the INI file allows for variables with whitespaces or
- in their names, such variables will cause errors as they are invalid
variable names in Python.
The test cases are defined in Python source files utilizing the unittest module,
thus every file must also be a valid Python file. Each file defining a test case
must start with test_ and have the file extension py. To be discovered by
the unittest module it must reside in a directory with a (empty) __init__.py
file.
A test case should test one logical unit, e.g. test for regressions of a certain bug or check if a command line option works. Each test case can run multiple commands which results are compared to an expected standard output, standard error and return value. Should differences arise or should one of the commands take too long, then an error message with the exact differences is shown to the user.
An example test case file would look like this:
# -*- coding: utf-8 -*- import system_tests class AnInformativeName(metaclass=system_tests.CaseMeta): filename = "invalid_input_file" commands = [ "$binary -c $import_file -i $filename" ] retval = ["$abort_exit_value"] stdout = ["Reading $filename"] stderr = [ """$abort_error error in $filename """ ]
The first 6 lines are necessary boilerplate to pull in the necessary routines to
run the actual tests (these are implemented in the module system_tests with
the meta-class system_tests.CaseMeta which performs the necessary preparations
for the tests to run). When adding new tests one should choose a new class name
that briefly summarizes the test. Note that the file name (without the
extension) with the directory structure is interpreted as the module by Python
and pre-pended to the class name when reporting about the tests. E.g. the file
regression/crashes/test_bug_15.py with the class OutOfBoundsRead gets
reported as regression.crashes.test_bug_15.OutOfBoundsRead already including
a brief summary of this test.
In the following lines the lists commands, retval, stdout and stderr
should be defined. These are lists of strings and must all have the same number
of elements.
The test suite at first takes all these strings and substitutes all values
following a $ with variables either defined in this class alongside (like
filename in the above example) or with the values defined in the test suite's
configuration file. Please note that defining a variable with the same name as a
variable in the suite's configuration file will result in an error (otherwise
one of the variables would take precedence leading to unexpected results). The
variables defined in the test suites configuration file are also available in
the system_tests namespace. In the above example it would be therefore
possible to access abort_exit_value via system_tests.abort_exit_value
(please be aware that all values will be strings though).
The substitution of values is performed using the template module from Python's
string library via safe_substitute. In the above example the command would
thus expand to:
/path/to/the/dir/build/bin/binary -c /path/to/the/dir/conf/main.cfg -i invalid_input_file
and similarly for stdout and stderr.
Once the substitution is performed, each command is run using Python's
subprocess module, its output is compared to the values in stdout and
stderr and its return value to retval. Please note that for portability
reasons the subprocess module is run with shell=False, thus shell expansions,
pipes and redirections into files will not work.
As the test cases are implemented in Python, one can take full advantage of
Python for the construction of the necessary lists. For example when 10 commands
should be run and all return 0, one can write retval = 10 * [0] instead of
writing 0 ten times. The same is of course possible for strings.
It is generally recommended to use Python's multiline strings (strings starting
and ending with three " instead of one ") for the elements of the commands
list, especially when the commands include " or escape sequences. Proper
escaping is tricky to get right in a platform independent way, as it depends on
the terminal that is used. Using multiline strings circumvents this issue.
There are however some peculiarities with multiline strings in Python. Normal
strings start and end with a single " but multiline strings start with three
". Also, while the variable names must be indented, new lines in multiline
strings must not or additional whitespaces will be added. E.g.:
stderr = [ """something else""" ]
will actually result in the string:
something
else
and not:
something else
as the indentation might have suggested.
Also note that in this example the string will not be terminated with a newline
character. To achieve that put the """ on the following line.
Some test cases require the specification of paths (e.g. to the location of test
cases). This can be problematic when working with the Windows operating system,
as it sometimes exhibits problems with / as path separators instead of \,
which cannot be used on every other platform.
This can be circumvented by creating the paths via os.path.join, but that is
quite verbose. A slightly simpler alternative is the function path from
system_tests which converts all / inside your string into the platform's
default path separator:
# -*- coding: utf-8 -*- from system_tests import CaseMeta, path class AnInformativeName(metaclass=CaseMeta): filename = path("$path_to_test_files/invalid_input_file") # the rest of your test case
This section describes more advanced features that are probably not necessary the "standard" usage of the test suite.
The test suite supports providing a standard input to commands in a similar
fashion as the standard output and error are specified: it expects a list (with
the length equal to the number of commands) of standard inputs (either strings
or bytes). For commands that expect no standard input, simply set the
respective entry to None:
# -*- coding: utf-8 -*- import system_tests class AnInformativeName(metaclass=system_tests.CaseMeta): commands = [ "$binary -c $import_file --", "$binary -c $import_file --" ] retval = [1, 1] stdin = [ "read file a", None ] stdout = [ "Reading...", "" ] stderr = [ "Error", "No input provided" ]
In this example, the command $binary -c $import_file -- would be run twice,
first with the standard input read file a and second without any input
(resulting in the error No input provided).
If all commands don't expect any standard input, omit the attribute stdin, the
test suite will implicitly assume None for every command.
The test suite will try to interpret the program's output as utf-8 encoded
strings and if that fails it will try the iso-8859-1 encoding (also know as
latin-1).
If the tested program outputs characters in another encoding then it can be
supplied as the encodings parameter in each test case:
# -*- coding: utf-8 -*- import system_tests class AnInformativeName(metaclass=system_tests.CaseMeta): encodings = ['ascii'] filename = "invalid_input_file" commands = [ "$binary -c $import_file -i $filename" ] retval = ["$abort_exit_value"] stdout = ["Reading $filename"] stderr = [ """$abort_error error in $filename """ ]
The test suite will try to decode the program's output with the provided encodings in the order that they appear in the list. It will select the first encoding that can decode the output successfully. If no encoding is able to decode the program's output, then an error is raised. The list of all supported encodings can be found here.
Some programs output binary data directly to stdout or stderr. Such programs can
be also tested by specifying the type bytes as the only member in the
encodings list and supplying stdout and/or stderr as bytes and not as a
string.
An example test case would look like this:
# -*- coding: utf-8 -*- import system_tests class AnInformativeName(metaclass=system_tests.CaseMeta): encodings = [bytes] commands = ["$prog --dump-binary"] retval = [1] stdout = [bytes([1, 2, 3, 4, 16, 42])] stderr = [bytes()]
Using the bytes encoding has the following limitations:
- variables of the form $some_var cannot be expanded in stdout and stderr
- if the bytes encoding is specified, then both stderr and stdout must be
valid bytes
The test suite supports setting or modifying environment variables for
individual test cases. This can be accomplished by adding a member dictionary
named env with the appropriate variable names and keys:
# -*- coding: utf-8 -*- from system_tests import CaseMeta, path class AnInformativeName(metaclass=CaseMeta): env = { "MYVAR": 26, "USER": "foobar" } # if you want a pristine environment, consisting only of MYVAR & USER, # uncomment the following line: # inherit_env = False # the rest of the test case follows
All commands belonging to this test case will be run with a modified environment
where the variables MYVAR and USER will be set to the specified
values. By default the environment is inherited from the user's environment and
the specified variables in env take precedence over the variables in the
user's environment (in the above example the variable $USER would be
overridden). If no variables should be inherited set inherit_env to False
and your test case will get only the specified environment variables.
For tests that modify their input file it is useful to run these with a disposable copy of the input file and not with the original. For this purpose the test suite features a decorator which creates a copy of the supplied files and deletes the copies after the test ran.
Example:
# -*- coding: utf-8 -*- import system_tests @system_tests.CopyFiles("$filename", "$some_path/another_file.txt") class AnInformativeName(metaclass=system_tests.CaseMeta): filename = "invalid_input_file" commands = [ "$binary -c $import_file -i $filename" ] retval = ["$abort_exit_value"] stdout = ["Reading $filename"] stderr = [ """$abort_error error in $filename """ ]
In this example, the test suite would automatically create a copy of the files
invalid_input_file and $some_path/another_file.txt (some_path would be of
course expanded too) named invalid_input_file_copy and
$some_path/another_file_copy.txt. After the test ran, the copies are
deleted. Please note that variable expansion in the filenames is possible.
Some tests do not require a "brute-force" comparison of the whole output of a program but only a very simple check (e.g. that a string is present). For these cases, one can customize how stdout and stderr checked for errors.
The system_tests.Case class has two public functions for the check of stdout &
stderr: compare_stdout & compare_stderr. They have the following interface:
compare_stdout(self, i, command, got_stdout, expected_stdout) compare_stderr(self, i, command, got_stderr, expected_stderr)
with the parameters:
- i: index of the command in the commands list
- command: a string of the actually invoked command
- got_stdout/stderr: the obtained stdout, post-processed depending on the
platform so that lines always end with \n
- expected_stdout/stderr: the expected output extracted from
self.stdout/self.stderr
These functions can be overridden in child classes to perform custom checks (or to omit them completely, too). Please however note, that it is not possible to customize how the return value is checked. This is indented, as the return value is often used by the OS to indicate segfaults and ignoring it (in combination with flawed checks of the output) could lead to crashes not being noticed.
A drop-in replacement for compare_stderr is provided by the system_tests
module itself: check_no_ASAN_UBSAN_errors. This function only checks that
errors from AddressSanitizer and undefined behavior sanitizer are not present in
the obtained output to standard error and nothing else. This is useful for
test cases where stderr is filled with warnings that are not worth being tracked
by the test suite. It can be used in the following way:
# -*- coding: utf-8 -*- import system_tests class AnInformativeName(metaclass=system_tests.CaseMeta): filename = "invalid_input_file" commands = ["$binary -c $import_file -i $filename"] retval = ["$abort_exit_value"] stdout = ["Reading $filename"] stderr = ["""A huge amount of error messages would be here that we absolutely do not care about. Actually everything in this string gets ignored, so we can just leave it empty. """ ] compare_stderr = system_tests.check_no_ASAN_UBSAN_errors
The test suite can run all commands under a memory checker like
valgrind or dr. memory. This
option can be enabled by adding the entry memcheck in the General section of
the configuration file, which specifies the command to invoke the memory
checking tool. The test suite will then prefix all commands with the
specified command.
For example this configuration file:
[General] timeout: 0.1 memcheck: valgrind --quiet
will result in every command specified in the test cases being run as valgrind
--quiet $command.
When running your test cases under a memory checker, please take the following into account:
valgrind and dr. memory slow the program execution down by a factor of
10-20. Therefore the test suite will increase the timeout value by a factor of
20 or by the value specified in the option memcheck_timeout_penalty in the
General section.
valgrind reports by default on success to stderr, be sure to run it with
--quiet. Otherwise successful tests will fail under valgrind, as unexpected
output is present on stderr
valgrind and ASAN cannot be used together
Although the option is called memcheck, it can be used to execute all
commands via a wrapper that has a completely different purpose (e.g. to
collect test coverage).
In case completely custom checks have to be run but one still wants to access
the variables from the test suite, the class system_test.Case provides the
function expand_variables(self, string). It performs the previously described
variable substitution using the test suite's configuration file.
Unfortunately, it has to run in a class member function. The setUp() function
can be used for this, as it is run before each test. For example like this:
class SomeName(metaclass=system_tests.CaseMeta): def setUp(self): self.commands = [self.expand_variables("$some_var/foo.txt")] self.stderr = [""] self.stdout = [self.expand_variables("$success_message")] self.retval = [0]
This example will work, as the test runner reads the data for commands,
stderr, stdout and retval from the class instance. What however will not
work is creating a new member in setUp() and trying to use it as a variable
for expansion, like this:
class SomeName(metaclass=system_tests.CaseMeta): def setUp(self): self.new_var = "foo" self.another_string = self.expand_variables("$new_var")
This example fails in self.expand_variables because the expansion uses only
static class members (which new_var is not). Also, if you modify a static
class member in setUp() the changed version will not be used for variable
expansion, as the variables are saved in a new dictionary before setUp()
runs. Thus this:
class SomeName(metaclass=system_tests.CaseMeta): new_var = "foo" def setUp(self): self.new_var = "bar" self.another_string = self.expand_variables("$new_var")
will result in another_string being "foo" and not "bar".
The Case class provides two hooks that are run after each command and after
all commands, respectively. The hook which is run after each successful command
has the following signature:
post_command_hook(self, i, command)
with the following parameters:
- i: index of the command in the commands list
- command: a string of the actually invoked command
The hook which is run after all test takes no parameters except self:
post_tests_hook(self)
By default, these hooks do nothing. They can be used to implement custom checks after certain commands, e.g. to check if a file was created. Such a test can be implemented as follows:
# -*- coding: utf-8 -*- import system_tests class AnInformativeName(metaclass=system_tests.CaseMeta): filename = "input_file" output = "out" commands = ["$binary -o output -i $filename"] retval = [0] stdout = [""] stderr = [""] output_contents = """Hello World! """ def post_tests_hook(self): with open(self.output, "r") as out: self.assertMultiLineEqual(self.output_contents, out.read(-1))
setUpClass() function for the test
cases. setUpClass() is used by system_tests.Case to store the variables
for expansion.The test suite is written for Python 3 and is not compatible with Python 2, thus
it must be run with python3 and not with python (which is usually an alias
for Python 2).
Then navigate to the tests/ subdirectory and run:
python3 runner.py
One can supply the script with a directory where the suite should look for the tests (it will search the directory recursively). If omitted, the runner will look in the directory where the configuration file is located. It is also possible to instead pass a file as the parameter, the test suite will then only run the tests from this file.
The runner script also supports the optional arguments --config_file which
allows to provide a different test suite configuration file than the default
suite.conf. It also forwards the verbosity setting via the -v/--verbose
flags to Python's unittest module.
Optionally one can provide the --debug flag which will instruct test suite to
print all command invocations and all expected and obtained outputs to the
standard output.