User Guide

Platform detection

It’s very common to have one set of logic for Windows and another for all non-Windows (Unix-based) platforms, and PySys has a dedicated constant pysys.constants.IS_WINDOWS for that:

self.startProcess('cmd.exe' if IS_WINDOWS else 'bash', ...)

For finer grained platform detection we recommend using the facilities built into Python, for example sys.platform, platform.platform() or platform.uname().

Skipping tests

If your logic detects that a test should not be executed for this platform or mode, simply use self.skipTest(...) near the top of the test’s execute() method, specifying the reason for the skip:

self.skipTest('MyFeature is not supported on Windows')

As well as setting the test outcome and reason, this will raise an exception ensuring that the rest of execute() and validate() do not get executed.

Alternatively if the test should be skipped regardless of platform/mode etc, it is best to specify that statically in your pysystest.xml file:

<skipped reason="Skipped until bug #12345 is fixed"/>

Checking for error messages in log files

The BaseTest.assertGrep() method is an easy way to check that there are no error messages in log files from processes started by PySys. Rather than checking for an expression such as ' ERROR: ', it is recommended to define your expression so that the error message itself is included, e.g.:

self.assertGrep('myprocess.log', expr=' ERROR: .*', contains=False)

This approach ensures that the error message itself is included in the test’s console output, run.log and the summary of failed test outcomes, which avoids the need to open up the individual logs to find out what happened, and makes it much easier to triage test failures, especially if several tests fail for the same reason.

Sharing logic across tests using plugins

Often you will have some standard logic that needs to be used in the execute or validation of many/all testcases, such as starting the application you’re testing, or checking log files for errors.

The recommended way to do that in PySys is to create one or more “plugins”. There are currently several kinds of plugin:

  • test plugins; instances of test plugins are created for each BaseTest that is instantiated, which allows them to operate independently of other tests, starting and stopping processes just like code in the BaseTest class would. Test plugins are configured with <test-plugin classname="..." alias="..."/> and can be any Python class provided it has a method setup(self, testobj) (and no constructor arguments). As the plugins are instantiated just after the BaseTest subclass, you can use them any time after (but not within) your test’s __init__() constructor (for example, in BaseTest.setup()).

  • runner plugins; these are instantiated just once per invocation of PySys, by the BaseRunner, before pysys.baserunner.BaseRunner.setup() is called. Unlike test plugins, any processes or state they maintain are shared across all tests. These can be used to start servers/VMs that are shared across tests. Runner plugins are configured with <runner-plugin classname="..." alias="..."/> and can be any Python class provided it has a method setup(self, runner) (and no constructor arguments).

    Runner plugins that generate output files/directories should by default put that output under either the runner.output directory, or (for increased prominence) the runner.output+'/..' directory (which is typically testRootDir unless an absolute --outdir path was provided).

  • writer plugins: this kind of plugin has existed in PySys for many releases and are effectively a special kind of runner plugin with extra callbacks to allow them to write test results and/or output files to a variety of destinations. Writers must implement a similar but different interface to other runner plugins; see pysys.writer for details. They can be used for everything from writing test outcome to an XML file, to archiving output files, to collecting files from each test output and using them to generate a code coverage report during cleanup at the end of the run.

To make your plugin configurable, add a static field for each plugin property, which defines the default value and (implicitly) the type. After construction of each plugin, an attribute is assigned with the actual value of each plugin property so each property can be accessed using self.propname (by the time the plugin’s setup method is called). In addition to plugin properties, pysys run -Xkey=value command line options for the plugin (if needed) can be accessed using the runner’s pysys.baserunner.BaseRunner.getXArg() method.

A test plugin could look like this:

class MyTestPlugin(object):
        myPluginProperty = 'default value'
        Example of a plugin configuration property. The value for this plugin instance can be overridden using ``<property .../>``.
        Types such as boolean/list[str]/int/float will be automatically converted from string.

        def setup(self, testObj):
                self.owner = self.testObj = testObj
                self.log = logging.getLogger('pysys.myorg.MyRunnerPlugin')
      'Created MyTestPlugin instance with myPluginProperty=%s', self.myPluginProperty)

                # there is no standard cleanup() method, so do this if you need to execute something on cleanup:

        def __myPluginCleanup(self):
      'Cleaning up MyTestPlugin instance')

        # An example of providing a method that can be accessed from each test
        def getPythonVersion(self):
                self.owner.startProcess(sys.executable, arguments=['--version'], stdouterr='MyTestPlugin.pythonVersion')
                return self.owner.waitForGrep('MyTestPlugin.pythonVersion.out', '(?P<output>.+)')['output'].strip()

        # A common pattern is to create a helper method that you always call from your `BaseTest.validate()`
        # That approach allows you to later customize the logic by changing just one single place, and also to omit
        # it for specific tests where it is not wanted.
        def checkLogsForErrors(self):
                self.assertGrep('myapp.log', ' ERROR .*', contains=False)

With configuration like this:

        <test-plugin classname="myorg.testplugin.MyTestPlugin" alias="myalias">
                    <property name="myPluginProperty" value="my value"/>

… you can now access methods defined by the plugin from your tests using self.myalias.getPythonVersion().

Alternatively, you can create a trivial BaseTest subclass that instantiates plugins in code (rather than XML) which would allow code completion (if your editor of choice supports this) but still provide the benefits of the modular composition approach.

You can add any number of test and/or runner plugins to your project, perhaps a mixture of custom plugins specific to your application, and third party PySys plugins supporting standard tools and languages.

In addition to the alias-based lookup, plugins can get a list of the other plugin instances using self.testPlugins (from BaseTest) or self.runnerPlugins (from pysys.baserunner.BaseRunner), which provides a way for plugins to reference each other without depending on the aliases that may be in use in a particular project configuration.

When creating a runner plugin you may need somewhere to put output files, logs etc. Plugins that generate output files/directories should by default put that output in a dedicated directory either the runner.output directory, or (for increased prominence if it’s something users will look at a lot) a directory one level up e.g. runner.output+'/../myplugin' (which is typically under testRootDir unless an absolute --outdir path was provided) . A prefix of double underscore __pysys is recommended under testRootDir to distinguish dynamically created directories (ignored by version control) from the testcase directories (checked into version control).

For examples of the project configuration, including how to set plugin-specific properties that will be passed to its constructor, see the sample Project Configuration file.

Configuring and overriding test options

PySys provides two mechanisms for specifying options such as credentials, hostnames, or test duration/iteration that you might want to change or override when running tests:

  • Testcase attributes, which are just variables on the Python testcase instance (or a BaseTest subclass shared by many tests). Attributes can be overridden on the command line using pysys run -Xattr=value.

    Attributes are useful for settings specific to an individual testcase such as the number of iterations or time duration to use for a performance test. A user running the test locally you might want to temporarily set to a lower iteration count while getting the test right, or perhaps try a higher value to get a more stable performance result.

  • Project properties. The default value is specified in the pysysproject.xml file or in a .properties file referenced from it.

    Properties can be overridden using an environment variable. Project properties are useful for things like credentials and hostnames that are shared across many testcases, and where you might want to set up customizations in your shell so that you don’t need to keep specifying them every time you invoke pysys run.

To use a testcase attribute, set the default value on your test or basetest as a static attribute on the test class, for example:

class PySysTest(BaseTest):

        myIterationCount = 100*1000 # can be overridden with -XmyIterationCount=

        def execute(self):
      'Using iterations=%d', self.myIterationCount)

Once the default value is defined with a static attribute, you can override the value when you run your test using the -X option:

pysys run -XmyIterationCount=10

If the attribute was defined with a default value of int, float, bool or list then the -X value will be automatically converted to that type; otherwise, it will be a string.

If instead of setting a default for just one test you wish to set the default for many tests from your custom BaseTest subclass, then you would do the same thing in the definition of that BaseTest subclass. If you don’t have a custom BaseTest class, you can use self.runner.getXArg() from any plugin to get the value or default, with the same type conversion described above.

The other mechanism that PySys supports for configurable test options is project properties.

To use a project property that can be overridden with an environment variable, add a property element to your pysysproject.xml file:

<property name="myCredentials" value="${env.MYCOMPANY_CREDENTIALS}" default="testuser:testpassword"/>

This property can will take the value of the specified environment variable, or else the default if any undefined properties/env vars are included in value. Note that if the value contains unresolved variables and there is no valid default, the project will fail to load.

You may want to set the attribute pathMustExist="true" when defining properties that refer to a path such as a build output directory that should always be present.

Another way to specify default project property values is to put them into a Java-style .properties file. You can use properties to specify which file is loaded, so it would be possible to customize using environment variables:

<property name="myProjectPropertiesFile" value="${env.MYCOMPANY_CUSTOM_PROJECT_PROPERTIES}" default="${testRootDir}/"/>
<property file="${myProjectPropertiesFile}" pathMustExist="true"/>

To use projects properties in your testcase, just access the attributes on self.project from either a test instance or a runner:

def execute(self):'Using username=%s and password %s' % self.project.myCredentials.split(':'))

Property properties will always be of string type.

Producing code coverage reports

PySys can be extended to produce code coverage reports for any language, by creating a writer plugin.

There is an existing writer that produces coverage reports for programs written in Python called pysys.writer.testoutput.PythonCoverageWriter, which uses the library. To use this you need to add the <writer> to your project (see the sample pysysproject.xml for an example) and make sure you’re starting your Python processes with coverage support enabled, by using BaseTest.startPython.

The usual way to enable code coverage (for all supported languages) is to set -XcodeCoverage when running your tests (or to run with --ci which does this automatically). Individual writers may additionally provide their own properties to allow fine-grained control e.g. -XpythonCoverage=true/false.

Be sure to add the disableCoverage group to any tests (or test directories) that should not use coverage, such as performance tests.

If you wish to produce coverage reports using any other language, this is easy to achieve by following the same pattern:

  • When your tests start the program(s) whose coverage is to be measured, add the required arguments or environment variables to enable coverage using the coverage tool of your choice. The most convenient place to put helper methods for starting your application is in a custom test plugin class.

    When starting your process, you can detect whether to enable code coverage like this:

    if self.runner.getBoolProperty(‘mylanguageCoverage’, default=self.runner.getBoolProperty(‘codeCoverage’)) and not self.disableCoverage:

    Often you will need to set an environment variable to indicate the filename that coverage should be generated under. Make sure to use a unique filename so that multiple processes started by the same test do not clash. Often you will need to ensure that your application is shutdown cleanly (rather than being automatically killed at the end of the test) so that it has a chance to write the code coverage information.

  • Create a custom writer class which collects coverage files (matching a specific regex pattern) from the output directory. The usual way to do this would be to subclass pysys.writer.testoutput.CollectTestOutputWriter. Configure default values for main configuration properties (by defining them as static variables in your class). Then implement pysys.writer.api.BaseResultsWriter.isEnabled() to define when coverage reporting will happen, and run the required processes to combine coverage files and generate a report in the destDir in pysys.writer.api.BaseResultsWriter.cleanup(), which will execute after all tests have completed.

    Finally, add the new writer class to your pysysproject.xml file.

  • Add the disableCoverage group to any tests (or test directories) that should not use coverage, such as performance tests.

  • If using a continuous integration system or centralized code coverage database, you could optionally upload the coverage data there from the directory PySys collected it into, so there is a permanent record of any changes in coverage over time. The artifact publishing capability of pysys.writer.testoutput.CollectTestOutputWriter will help with that.

Running tests in multiple modes

One of the most powerful features of PySys is the ability to run the same test in multiple modes from a single execution. This could be useful for cases such as a web test that needs to pass against multiple supported web browsers, or a set of tests that should be run against various different database but can also be run against a mocked database for quick local development.

Using modes is fairly straightforward. First edit the pysystest.xml files for tests that need to run in multiple modes, and add a list of the supported modes:

     <modes inherit="true">

When naming modes, TitleCase is recommended, and dot and underscore characters may be used; typically dot is useful for version numbers and underscore is useful for separating out different dimensions e.g. database vs web browser as in the above example. PySys will give an error if you use different capitalization for the same mode in different places, as this would likely result in test bugs.

The first mode listed is designated the “primary” mode which means it’s the one that is used by default when running your tests without a --mode argument. It’s best to choose either the fastest mode or else the one that is most likely to show up interesting issues as the primary mode.

In large projects you may wish to configure modes in a pysysdirconfig.xml file in a parent directory rather than in pysystest.xml, which will by default be inherited by all nested testcases (unless inherit="false" is specified in the <modes> element), and so there’s a single place to edit the modes list if you need to change them later. It’s also possible to create a custom DescriptorLoader subclass that dynamically adds modes from Python code, perhaps based on the groups specified in each descriptor or runtime information such as the current operating system.

You can find the mode that this test is running in using self.mode. To ensure typos and inconsistencies in individual test descriptor modes do no go unnoticed, it is best to provide constants for the possible mode values and/or do validation and unpacking of modes in a test plugin like this:

class MyTestPlugin(object):
        def setup(self, testObj):
                # Unpack and validate mode
                testObj.databaseMode, testObj.browserMode = testObj.mode.split('_')
                assert testObj.browserMode in ['Chrome', 'Firefox'], testObj.browserMode

                # This is a convenient pattern for specifying the method or class
                # constructor to call for each mode, and to get an exception if an
                # invalid mode is specified
                dbHelperFactory = {
                        'MockDatabase': MockDB,
                        'MyDatabase2.0': lambda: self.startMyDatabase('2.0')
                # Call the supplied method to start/configure the database
                testObj.db = dbHelperFactory()

Finally, PySys provides a rich variety of pysys run arguments to control which modes your tests will run with. By default it will run every test in its primary mode (for tests with no mode, the primary mode is self.mode==None) - which is great for quick checks during development of your application and testcases.

Your main test run (perhaps in a CI job) probably wants to run tests in all modes:

pysys run --mode ALL --threads auto

You can also specify specifies modes to run in, or to run everything except specified modes:

pysys run --mode MyMode1,MyMode2
pysys run --mode !MyMode3,!MyMode4

After successfully getting all your tests passing in their primary mode, it could be useful to run them in every mode other than the primary one:

pysys run --mode !PRIMARY

For reporting purposes, all testcases must have a unique id. With a multiple mode test this is achieved by having the id automatically include a ~Mode suffix. If you are reporting performance results from a multi-mode test, make sure you include the mode in the resultKey when you all BaseTest.reportPerformanceResult, since the resultKey must be globally unique.

In addition to the --mode argument which affects all selected tests, it is possible to run a specific test in a specific mode. This can be useful when you have a few miscellaneous test failures and just want to re-run the failing tests:

pysys run MyTest_001~MockDatabase MyTest_020~MyDatabase_2.0

Test ids and structuring large projects

Each test has a unique id which is used in various places such as when reporting passed/failed outcomes. By default the id is just the name of the directory containing the pysystest.xml file.

You can choose a suitable naming convention for your tests. For example, you might wish to differentiate with just a numeric suffix such as:


This has the benefit that it’s easy to refer to tests when communicating with other developers, and that you can run tests on the command line by specifying just a number, but you have to look at the test title to discover what it does.

Alternatively you could choose to use a semantically meaningful name for each test:


These test ids are easier to understand but can’t be referred to as concisely.

Whatever scheme you use for naming test ids, if you have a large set of tests you will want to separate them out into different directories, so that related tests can be executed and maintained together. You might have different directories for different subsystems/parts of your application, and/or for different kinds of testing:

/  (root dir containing pysysproject.xml)



It is important to ensure every test has a unique id. Although it would be possible to do this by convention in the individual test directory names, this is fragile and could lead to clashes if someone forgets. Therefore for large projects it is usually best to add a pysysdirconfig.xml file to provide default configuration for each directory of testcases.

For example, in SubSystem1/performance you could create a pysysdirconfig.xml file containing:

<?xml version="1.0" encoding="utf-8"?>

        <groups inherit="true">

        <modes inherit="true">


  <execution-order hint="-100.0"/>

  <!-- Uncomment this to mark all tests under this directory as skipped
        (overrides the state= attribute on individual tests). -->
  <!-- <skipped reason=""/> -->


This serves several useful purposes:

  • It adds a prefix “SubSystem1_perf.” to the beginning of the test directory names to ensure there’s a unique id for each one with no chance of conflicts across different directories.

  • It adds groups that make it possible to run all your performance tests, or all your tests for a particular part of the application, in a single command.

  • It disables code coverage instrumentation which could adversely affect your performance results.

  • It specifies that the performance tests will be run with a lower priority, so they execute after more urgent (and quicker) tests such as unit tests.

  • It provides the ability to temporarily skip a set of tests if they are broken temporarily pending a bug fix.

By default both modes and groups are inherited from pysysdirconfig.xml files in parent directories, but inheriting can be disabled in an individual descriptor by setting inherit="false", in case you have a few tests that only make sense in one mode. Alternatively, you could allow the tests to exist in all modes but call self.skipTest <BaseTest.skipTest> at the start of the test BaseTest.execute method if the test cannot execute in the current mode.

See the pysysdirconfig.xml sample in pysys/xml/templates/dirconfig for a full example of a directory configuration file.

Controlling execution order

In large projects where the test run takes several hours or days, you may wish to control the order that PySys executes different groups of tests - or tests with different modes, to maximize the chance of finding out quickly if something has gone wrong, and perhaps to prioritize running fast unit and correctness tests before commencing on longer running performance or soak tests.

By default, PySys runs tests based on the sorting them by the full path of the pysystest.xml files. If you have tests with multiple modes, PySys will run all tests in their primary mode first, then any/all tests which list a second mode, followed by 3rd, 4th, etc.

All of this can be customized using the concept of an execution order hint. Every test descriptor is assigned an execution order hint, which is a positive or negative floating point number which defaults to 0.0, and is used to sort the descriptors before execution. Higher execution order hints mean later execution. If two tests have the same hint, PySys falls back on using the path of the pysystest.xml file to determine a canonical order.

The hint for each test is generated by adding together hint components from the following:

  • A test-specific hint from the pysystest.xml file’s <execution-order hint="..."/>. If the hint is blank (the default), the test inherits any hint specified in a pysysdirconfig.xml file in an ancestor folder, or 0.0 if there aren’t any. Note that hints from pysysdirconfig.xml files are not added together; instead, the most specific wins.

  • All <execution-order> elements in the project configuration file which match the mode and/or group of the test. The project configuration is the place to put mode-specific execution order hints, such as putting a particular database or web browser mode earlier/later. See the sample pysysproject.xml file for details.

  • For multi-mode tests, the secondaryModesHintDelta specified in the project configuration (unless it’s set to zero), multiplied by a number indicating which mode this is. If a test had 3 modes Mode1, Mode2 and Mode3 then the primary mode (Mode1) would get no additional hint, Mode2 would get secondaryModesHintDelta added to its hint and Mode3 would get 2 x secondaryModesHintDelta added to its hint. This is the mechanism PySys uses to ensure all tests run first in their primary mode before any tests run in their secondary modes. Usually the default value of secondaryModesHintDelta = +100.0 is useful and avoids the need for too much mode-specific hint configuration (see above). However if you prefer to turn it off to have more manual control - or you prefer each test to run in all modes before moving on to the next test - then simply set secondaryModesHintDelta to 0.

For really advanced cases, you can programmatically set the executionOrderHint on each descriptor by providing a custom pysys.xml.descriptor.DescriptorLoader or in the constructor of a custom pysys.baserunner.BaseRunner class.