Aggregating code coverage from several executions of phpunit

Use the "--coverage-php" option to PHPUnit to get it to write the coverage data as a serialized PHP_CodeCoverage object, then combine them using PHP_CodeCoverage::merge, like this:

<?php
/**
 * Deserializes PHP_CodeCoverage objects from the files passed on the command line,
 * combines them into a single coverage object and creates an HTML report of the
 * combined coverage.
 */

if ($argc <= 2) {
  die("Usage: php generate-coverage-report.php cov-file1 cov-file2 ...");
}

// Init the Composer autoloader
require realpath(dirname(__FILE__)) . '/../vendor/autoload.php';

foreach (array_slice($argv, 1) as $filename) {
  // See PHP_CodeCoverage_Report_PHP::process
  // @var PHP_CodeCoverage
  $cov = unserialize(file_get_contents($filename));
  if (isset($codeCoverage)) {
    $codeCoverage->filter()->addFilesToWhitelist($cov->filter()->getWhitelist());
    $codeCoverage->merge($cov);
  } else {
    $codeCoverage = $cov;
  }
}

print "\nGenerating code coverage report in HTML format ...";

// Based on PHPUnit_TextUI_TestRunner::doRun
$writer = new PHP_CodeCoverage_Report_HTML(
  'UTF-8',
  false, // 'reportHighlight'
  35, // 'reportLowUpperBound'
  70, // 'reportHighLowerBound'
  sprintf(
    ' and <a href="http://phpunit.de/">PHPUnit %s</a>',
    PHPUnit_Runner_Version::id()
      )
  );

$writer->process($codeCoverage, 'coverage');

print " done\n";
print "See coverage/index.html\n";

You may also be able to merge the files using a tool named phpcov, as described here: https://github.com/sebastianbergmann/phpunit/pull/685

I don't know how to do that with PHPUnit directly. To the extent that it produces test coverage data as an abstract set of pairs, it should be relatively easy to combine multiple sets of test coverage data in the abstract. Whether it does that, or whether that is easy, is another question.

Our PHP Test Coverage will collect test coverage data for any tests you care to run under any framework (including PHPUnit), and will allow you to easily combine coverage data from separate runs, out of the box. It will even verify when it is safe to do so (e.g., you haen't changed the source files).