diff -u b/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
--- b/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -179,7 +179,7 @@
 function simpletest_run_phpunit_tests($test_id, array $unescaped_test_classnames) {
   $phpunit_file = simpletest_phpunit_xml_filepath($test_id);
   $ret = simpletest_phpunit_run_command($unescaped_test_classnames, $phpunit_file);
-  if ($ret != 0) {
+  if ($ret) {
     // Something broke during the execution of phpunit.
     // Return an error record of all failed classes.
     $rows[] = [