Parallel testing for PHP

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4.1.1-alpha.2 2020-07-27 14:16 UTC


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The objective of ParaTest is to support parallel testing in PHPUnit. Provided you have well-written PHPUnit tests, you can drop paratest in your project and start using it with no additional bootstrap or configurations!


Why use paratest over the alternative parallel test runners out there?

  • Code Coverage report combining. Run your tests in N parallel processes and all the code coverage output will be combined into one report.
  • Zero configuration. After composer install, run with vendor/bin/paratest -p4 path/to/tests. That's it!
  • Flexible. Isolate test files in separate processes or take advantage of WrapperRunner for even faster runs.


To install with composer run the following command:

composer require --dev brianium/paratest


PHPUnit Version Corresponding Paratest Version
<= 6.* 1.*
7.* 2.*
8.* 3.*
9.* 4.*


After installation, the binary can be found at vendor/bin/paratest. Usage is as follows:

 paratest [-p|--processes PROCESSES] [-f|--functional] [--no-test-tokens] [-h|--help] [--coverage-clover COVERAGE-CLOVER] [--coverage-crap4j COVERAGE-CRAP4J] [--coverage-html COVERAGE-HTML] [--coverage-php COVERAGE-PHP] [--coverage-text] [--coverage-xml COVERAGE-XML] [-m|--max-batch-size MAX-BATCH-SIZE] [--filter FILTER] [--parallel-suite] [--passthru PASSTHRU] [--passthru-php PASSTHRU-PHP] [-v|--verbose VERBOSE] [--whitelist WHITELIST] [--phpunit PHPUNIT] [--runner RUNNER] [--bootstrap BOOTSTRAP] [-c|--configuration CONFIGURATION] [-g|--group GROUP] [--exclude-group EXCLUDE-GROUP] [--stop-on-failure] [--log-junit LOG-JUNIT] [--colors] [--testsuite [TESTSUITE]] [--path PATH] [--] [<path>]

 path                        The path to a directory or file containing tests. (default: current directory)
 --processes (-p)            The number of test processes to run. (Default: auto)
                             Possible values:
                             - Integer (>= 1): Number of processes to run.
                             - auto (default): Number of processes is automatically set to the number of logical CPU cores.
                             - half: Number of processes is automatically set to half the number of logical CPU cores.
 --functional (-f)           Run test methods instead of classes in separate processes.
 --no-test-tokens            Disable TEST_TOKEN environment variables. (Default: Variable is set)
 --help (-h)                 Display this help message.
 --coverage-clover           Generate code coverage report in Clover XML format.
 --coverage-crap4j           Generate code coverage report in Crap4J XML format.
 --coverage-html             Generate code coverage report in HTML format.
 --coverage-php              Serialize PHP_CodeCoverage object to file.
 --coverage-text             Generate code coverage report in text format.
 --coverage-xml              Generate code coverage report in PHPUnit XML format.
 --max-batch-size (-m)       Max batch size (only for functional mode). (Default: 0)
 --filter                    Filter (only for functional mode).
 --phpunit                   The PHPUnit binary to execute. (Default: vendor/bin/phpunit)
 --runner                    Runner, WrapperRunner or SqliteRunner. (Default: Runner)
 --bootstrap                 The bootstrap file to be used by PHPUnit.
 --configuration (-c)        The PHPUnit configuration file to use.
 --group (-g)                Only runs tests from the specified group(s).
 --exclude-group             Don't run tests from the specified group(s).
 --stop-on-failure           Don't start any more processes after a failure.
 --log-junit                 Log test execution in JUnit XML format to file.
 --colors                    Displays a colored bar as a test result.
 --testsuite                 Filter which testsuite to run. Run multiple suits by separating them with ",". Example:  --testsuite suite1,suite2
 --path                      An alias for the path argument.
 --parallel-suite            Run testsuites in parallel as opposed to running test classes / test functions in parallel.
 --passthru=PASSTHRU         Pass the given arguments verbatim to the underlying test framework. Example: --passthru="'--prepend' 'xdebug-filter.php'"
 --passthru-php=PASSTHRU-PHP Pass the given arguments verbatim to the underlying php process. Example: --passthru-php="'-d' ''"
  -v, --verbose=VERBOSE      If given, debug output is printed. Example: --verbose=1

Optimizing Speed

To get the most out of paratest, you have to adjust the parameters carefully.

  1. Adjust the number of processes with -p

    To allow full usage of your cpu cores, you should have at least one process per core. More processes allow better resource usage but keep in mind that each process has its own costs for spawning. The default is auto, which means the number of logical CPU cores is set as number of processes. You might try something like logical CPU cores * 2 (e.g. if you have 8 logical cores, you might try 16), but keep in mind that each process generates a little bit of overhead as well.

  2. Choose between per-testcase- and per-testmethod-parallelization with -f

    Given you have few testcases (classes) with many long running methods, you should use the -f option to enable the functional mode and allow different methods of the same class to be executed in parallel. Keep in mind that the default is per-testcase-parallelization to address inter-testmethod dependencies. Note that in most projects, using -f is slower since each test method will need to be bootstrapped separately.

  3. Use the WrapperRunner or SqliteRunner if possible

    The default Runner for PHPUnit spawns a new process for each testcase (or method in functional mode). This provides the highest compatibility but comes with the cost of many spawned processes and a bootstrapping for each process. Especially when you have a slow bootstrapping in your tests (like a database setup) you should try the WrapperRunner with --runner WrapperRunner or the SqliteRunner with --runner SqliteRunner. It spawns one "worker"-process for each parallel process (-p), executes the bootstrapping once and reuses these processes for each test executed. That way the overhead of process spawning and bootstrapping is reduced to the minimum.

  4. Tune batch max size --max-batch-size

    Batch size will affect on max amount of atomic tests which will be used for single test method. One atomic test will be either one test method from test class if no data provider available for method or will be only one item from dataset for method. Increase this value to reduce per-process overhead and in most cases it will also reduce parallel efficiency. Decrease this value to increase per-process overhead and in most cases it will also increase parallel efficiency. If amount of all tests less then max batch size then everything will be processed in one process thread so paratest is completely useless in that case. The best way to find the most effective batch size is to test with different batch size values and select best. Max batch size = 0 means that grouping in batches will not be used and one batch will equal to all method tests (one or all from data provider). Max batch size = 1 means that each batch will contain only one test from data provider or one method if data provider is not used. Bigger max batch size can significantly increase phpunit command line length so process can failed. Decrease max batch size to reduce command line length. Windows has limit around 32k, Linux - 2048k, Mac OS X - 256k.


Examples assume your tests are located under ./test/unit.

# Run all unit tests in 8 parallel processes
vendor/bin/paratest -p8 test/unit
# Run all unit tests in 4 parallel processes with WrapperRunner and output html code coverage report to /tmp/coverage
# (Code coverage requires Xdebug to be installed)
vendor/bin/paratest -p4 --runner=WrapperRunner --coverage-html=/tmp/coverage test/unit


If you run into problems with paratest, try to get more information about the issue by enabling debug output via --verbose=1.

In case you are using the WrapperRunner for execution, consider enabling logging for troubleshooting via export PT_LOGGING_ENABLE="true". The corresponding logfiles are placed in your sys_get_temp_dir().

See Logging docs for further information.

Generating code coverage

Examples assume your tests are located under ./test/unit.

vendor/bin/paratest -p 1 --coverage-text test/unit

Running phpunit in 1 process with /codebase/paratest/vendor/phpunit/phpunit/phpunit

Configuration read from /codebase/paratest/phpunit.xml.dist

...............................................................  63 / 155 ( 40%)
............................................................... 126 / 157 ( 80%)

Time: 27.2 seconds, Memory: 8.00MB

OK (163 tests, 328 assertions)

Code Coverage Report:
  2019-01-25 09:41:26

  Classes: 22.86% (8/35)
  Methods: 49.47% (139/281)
  Lines:   59.38% (896/1509)

Caution: Generating coverage is an art in itself. Please refer to our extensive guide on setting up everything correctly for code coverage generation with paratest.


Windows users be sure to use the appropriate batch files.

An example being:

vendor\bin\paratest.bat --phpunit vendor\bin\phpunit.bat ...

ParaTest assumes PSR-0 for loading tests.

For convenience paratest windows version use 79 columns mode to prevent blank lines in standard 80x25 windows console.

PHPUnit Xml Config Support

When running PHPUnit tests, ParaTest will automatically pass the phpunit.xml or phpunit.xml.dist to the phpunit runner via the --configuration switch. ParaTest also allows the configuration path to be specified manually.

ParaTest will rely on the testsuites node of phpunit's xml configuration to handle loading of suites.

The following phpunit config file is used for ParaTest's test cases.

<?xml version="1.0" encoding="UTF-8"?>
<phpunit backupGlobals="false"
        <testsuite name="ParaTest Fixtures">

Test token

The TEST_TOKEN environment variable is guaranteed to have a value that is different from every other currently running test. This is useful to e.g. use a different database for each test:

if (getenv('TEST_TOKEN') !== false) {  // Using paratest
    $dbname = 'testdb_' . getenv('TEST_TOKEN');
} else {
    $dbname = 'testdb';

For Contributors: Testing paratest itself

Note that The display_errors php.ini directive must be set to stderr to run the test suite.

Before creating a Pull Request be sure to run all the necessary checks with make command.

For an example of ParaTest out in the wild check out the example.