public function aggregateCoverageInformation()
	{
		if ( !isset($_GET[self::TEST_ID_VARIABLE]) ) {
			return '';
		}

		$coverage = array();
		$filter = new \PHP_CodeCoverage_Filter();

		foreach ( $this->getDataDirectoryFiles() as $data_directory_file ) {
			$raw_coverage_data = unserialize(file_get_contents($data_directory_file));

			foreach ( $raw_coverage_data as $file => $lines ) {
				if ( !$filter->isFile($file) ) {
					continue;
				}

				if ( !isset($coverage[$file]) ) {
					$coverage[$file] = array('md5' => md5_file($file), 'coverage' => $lines);
				}
				else {
					foreach ( $lines as $line => $flag ) {
						if ( !isset($coverage[$file]['coverage'][$line])
							|| $flag > $coverage[$file]['coverage'][$line]
						) {
							$coverage[$file]['coverage'][$line] = $flag;
						}
					}
				}
			}
		}

		return serialize($coverage);
	}