Support automatic splitting tests across nodes

[JanTvrdik]

For example Circle CI can provide CIRCLE_NODE_INDEX and CIRCLE_NODE_TOTAL env. variables. Naive implementation of splitting can look like this.

class Runner
{
	...
	public function run()
	{
		...
		$nodeIndex = (int) getenv('CIRCLE_NODE_INDEX');
		$nodeTotal = (int) getenv('CIRCLE_NODE_TOTAL');
		if ($nodeTotal) {
			$this->jobs = array_values(array_filter(
				$this->jobs,
				function (int $jobIndex) use ($nodeIndex, $nodeTotal) {
					return ($jobIndex % $nodeTotal) === $nodeIndex;
				},
				ARRAY_FILTER_USE_KEY
			));
		}

Better implementation should automatically balance the tests based on the time it took to execute them in previous run.

[JanTvrdik]

Alternative (and quite possibly better approach) is to add new CLI option to print tests names to stdout and let them be processed by another tool.

For example Circle CI does provide picard tool to split the tests. So the final command would look sth like

tester --find-tests ./tests | picard | xargs tester -c ./tests/php.ini