Using PHP 7 to run tests, I find that occasionally a BenchmarkerTest fails with a "Division by 0" message. Usually just in just one test, but I've seen it happen in two as shown below.
Using PHP 7.0.27-1 PHPUnit 4.8.36 by Sebastian Bergmann and contributors. ..E..E. Time: 126 ms, Memory: 18.00MB There were 2 errors: 1) MediaWiki\Tests\Maintenance\BenchmarkerTest::testBenchVerbose Division by zero /usr/local/src/MediaWiki/core/maintenance/benchmarks/Benchmarker.php:103 /usr/local/src/MediaWiki/core/tests/phpunit/maintenance/BenchmarkerTest.php:75 /usr/local/src/MediaWiki/core/maintenance/doMaintenance.php:94 2) MediaWiki\Tests\Maintenance\BenchmarkerTest::testVerboseRun Division by zero /usr/local/src/MediaWiki/core/maintenance/benchmarks/Benchmarker.php:103 /usr/local/src/MediaWiki/core/tests/phpunit/maintenance/BenchmarkerTest.php:140 /usr/local/src/MediaWiki/core/maintenance/doMaintenance.php:94 FAILURES! Tests: 7, Assertions: 5, Errors: 2.
I wasn't able to get PHP5 or HHVM to do it in some quick attempts. Perhaps they're enough slower that they never wind up with a zero timing, or perhaps they have more accurate timers.