If I use the mediwiki/vendor repo to supply dependencies, I get the following:
```
$ phpcs
PHP Fatal error: Uncaught exception 'PHP_CodeSniffer_Exception' with message 'Referenced sniff "vendor/mediawiki/mediawiki-codesniffer/MediaWiki" does not exist' in /usr/share/php/PHP/CodeSniffer.php:1092
Stack trace:
#0 /usr/share/php/PHP/CodeSniffer.php(733): PHP_CodeSniffer->_expandRulesetReference(Object(SimpleXMLElement), '/usr/local/src/...', 0)
#1 /usr/share/php/PHP/CodeSniffer.php(551): PHP_CodeSniffer->processRuleset('/usr/local/src/...')
#2 /usr/share/php/PHP/CodeSniffer/CLI.php(818): PHP_CodeSniffer->initStandard(Array, Array)
#3 /usr/share/php/PHP/CodeSniffer/CLI.php(95): PHP_CodeSniffer_CLI->process()
#4 /usr/bin/phpcs(25): PHP_CodeSniffer_CLI->runphpcs()
#5 {main}
thrown in /usr/share/php/PHP/CodeSniffer.php on line 1092
```
Apparently mediawiki/vendor doesn't include whatever dependencies are needed to run phpcs. Now that phpcs is voting, it's a pain not to be able to run it locally.
If instead I use composer to install dependencies, phpcs works but phpunit fails some tests! For example:
```
$ php tests/phpunit/phpunit.php --configuration tests/phpunit/suite.xml tests/phpunit/includes/exception/ErrorPageErrorTest.php
PHPUnit already present
PHPUnit 3.7.37 by Sebastian Bergmann.
Configuration read from /usr/local/src/MediaWiki/core/tests/phpunit/suite.xml
EE.
Time: 124 ms, Memory: 13.25Mb
There were 2 errors:
1) ErrorPageErrorTest::testConstruction
Erroneous data format for unserializing 'Mock_Message_e3de1385'
/usr/local/src/MediaWiki/core/tests/phpunit/includes/exception/ErrorPageErrorTest.php:12
/usr/local/src/MediaWiki/core/tests/phpunit/includes/exception/ErrorPageErrorTest.php:23
/usr/local/src/MediaWiki/core/tests/phpunit/MediaWikiTestCase.php:137
2) ErrorPageErrorTest::testReport
Erroneous data format for unserializing 'Mock_Message_e3de1385'
/usr/local/src/MediaWiki/core/tests/phpunit/includes/exception/ErrorPageErrorTest.php:12
/usr/local/src/MediaWiki/core/tests/phpunit/includes/exception/ErrorPageErrorTest.php:33
/usr/local/src/MediaWiki/core/tests/phpunit/MediaWikiTestCase.php:137
FAILURES!
Tests: 3, Assertions: 1, Errors: 2.
```
With composer-managed vendor, it uses the ancient version of phpunit we have composer install. Which apparently has the issue described in https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=762095, phpunit-mock-objects 1.2.3 doesn't work with PHP 5.6.