diff --git a/core/modules/simpletest/simpletest.module b/core/modules/simpletest/simpletest.module
index 665b8baaba..f49a8c42bc 100644
--- a/core/modules/simpletest/simpletest.module
+++ b/core/modules/simpletest/simpletest.module
@@ -205,9 +205,9 @@ function simpletest_run_tests($test_list) {
  *   The parsed results of PHPUnit's JUnit XML output, in the format of
  *   {simpletest}'s schema.
  */
-function simpletest_run_phpunit_tests($test_id, array $unescaped_test_classnames, &$status = NULL) {
+function simpletest_run_phpunit_tests($test_id, array $unescaped_test_classnames, &$status = NULL, $environment_variables = []) {
   $phpunit_file = simpletest_phpunit_xml_filepath($test_id);
-  simpletest_phpunit_run_command($unescaped_test_classnames, $phpunit_file, $status, $output);
+  simpletest_phpunit_run_command($unescaped_test_classnames, $phpunit_file, $status, $output, $environment_variables);
 
   $rows = [];
   if ($status == TestStatus::PASS) {
@@ -219,7 +219,7 @@ function simpletest_run_phpunit_tests($test_id, array $unescaped_test_classnames
       'test_id' => $test_id,
       'test_class' => implode(",", $unescaped_test_classnames),
       'status' => TestStatus::label($status),
-      'message' => 'PHPunit Test failed to complete; Error: ' . $output,
+      'message' => 'PHPunit Test failed to complete; Error: ' . implode("\n", $output),
       'message_group' => 'Other',
       'function' => implode(",", $unescaped_test_classnames),
       'line' => '0',
@@ -356,14 +356,14 @@ function simpletest_phpunit_configuration_filepath() {
  * @return string
  *   The results as returned by exec().
  */
-function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpunit_file, &$status = NULL, &$output = NULL) {
+function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpunit_file, &$status = NULL, &$output = NULL, $environment_variables = []) {
   global $base_url;
   // Setup an environment variable containing the database connection so that
   // functional tests can connect to the database.
-  $process_environment_variables = [
+  $process_environment_variables = array_merge($environment_variables, [
     'SIMPLETEST_DB' => Database::getConnectionInfoAsUrl(),
     'SIMPLETEST_JUNIT_FILE' => $phpunit_file,
-  ];
+  ]);
 
   // Setup an environment variable containing the base URL, if it is available.
   // This allows functional tests to browse the site under test. When running
@@ -377,6 +377,8 @@ function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpun
 
   $command = [
     $phpunit_bin,
+    '--printer',
+    SimpletestUiPrinter::class,
   ];
 
   // Optimized for running a single test.
@@ -401,7 +403,7 @@ function simpletest_phpunit_run_command(array $unescaped_test_classnames, $phpun
   $process->inheritEnvironmentVariables();
   $process->setTimeout(NULL);
   $process->run();
-  $output = $process->getOutput();
+  $output = explode("\n", $process->getOutput());
   $status = $process->getExitCode();
 
   return '';
diff --git a/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php b/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php
index 30617b9560..7fda979f6f 100644
--- a/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php
+++ b/core/modules/simpletest/tests/src/Unit/SimpletestPhpunitRunCommandTest.php
@@ -54,6 +54,8 @@ protected function setUp() {
     $file_system = $this->prophesize(FileSystemInterface::class);
     // The simpletest directory wrapper will always point to /tmp.
     $file_system->realpath('public://simpletest')->willReturn(sys_get_temp_dir());
+    // The simpletest directory wrapper preparation will always be true.
+    $file_system->prepareDirectory(sys_get_temp_dir(), FileSystemInterface::CREATE_DIRECTORY | FileSystemInterface::MODIFY_PERMISSIONS)->willReturn(TRUE);
     $container->set('file_system', $file_system->reveal());
     \Drupal::setContainer($container);
   }
@@ -100,10 +102,8 @@ public function testSimpletestPhpUnitRunCommand($status, $label) {
       ]
     );
     $test_id = basename(tempnam(sys_get_temp_dir(), 'xxx'));
-    putenv('SimpletestPhpunitRunCommandTestWillDie=' . $status);
-    $ret = simpletest_run_phpunit_tests($test_id, [SimpletestPhpunitRunCommandTestWillDie::class]);
-    $this->assertSame($ret[0]['status'], $label);
-    putenv('SimpletestPhpunitRunCommandTestWillDie');
+    $ret = simpletest_run_phpunit_tests($test_id, [SimpletestPhpunitRunCommandTestWillDie::class], $status, ['SimpletestPhpunitRunCommandTestWillDie' => $status]);
+    $this->assertSame($label, $ret[0]['status']);
     unlink(simpletest_phpunit_xml_filepath($test_id));
   }