diff -u b/core/modules/config/lib/Drupal/config/Tests/ConfigSnapshotTest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigSnapshotTest.php
--- b/core/modules/config/lib/Drupal/config/Tests/ConfigSnapshotTest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigSnapshotTest.php
@@ -33,6 +33,9 @@
   public function setUp() {
     parent::setUp();
     $this->installSchema('system', 'config_snapshot');
+    // Update the config snapshot. This allows the parent::setUp() to write
+    // configuration files.
+    config_import_create_snapshot(\Drupal::service('config.storage'), \Drupal::service('config.storage.snapshot'));
   }
 
   /**
diff -u b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
--- b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
+++ b/core/modules/simpletest/lib/Drupal/simpletest/DrupalUnitTestBase.php
@@ -103,11 +103,11 @@
     $this->kernel->boot();
 
     // Create a minimal system.module configuration file so that the list of
-    // enabled modules can be maintained enabling
-    // \Drupal\Core\Config\ConfigInstaller::installDefaultConfig() to work.
-    \Drupal::config('system.module')
-      ->set('enabled', array())
-      ->save();
+    // enabled modules can be maintained allowing
+    // \Drupal\Core\Config\ConfigInstaller::installDefaultConfig() to work. Not
+    // using configuration factory ensures that events registered by modules
+    // during self::enableModules are registered.
+    \Drupal::service('config.cachedstorage.storage')->write('system.module', array('enabled' => array()));
 
     // Collect and set a fixed module list.
     $class = get_class($this);
@@ -275,12 +275,16 @@
     // Set the list of modules in the extension handler.
     $module_handler = $this->container->get('module_handler');
     $module_filenames = $module_handler->getModuleList();
-    $system_config = $this->container->get('config.factory')->get('system.module');
+    // Write directly to active storage to avoid early instantiation of
+    // services which can prevent modules from registering events.
+    $active_storage =  \Drupal::service('config.cachedstorage.storage');
+    $system_config = $active_storage->read('system.module');
     foreach ($modules as $module) {
       $module_filenames[$module] = drupal_get_filename('module', $module);
       // Maintain the list of enabled modules in configuration.
-      $system_config->set('enabled.' . $module, 0);
+      $system_config['enabled'][$module] = 0;
     }
+    $active_storage->write('system.module', $system_config);
     $module_handler->setModuleList($module_filenames);
     $module_handler->resetImplementations();
     // Update the kernel to make their services available.
@@ -294,7 +298,6 @@
     $this->pass(format_string('Enabled modules: %modules.', array(
       '%modules' => implode(', ', $modules),
     )));
-    $system_config->save();
   }
 
   /**
@@ -310,9 +313,12 @@
     // Unset the list of modules in the extension handler.
     $module_handler = $this->container->get('module_handler');
     $module_filenames = $module_handler->getModuleList();
+    $system_config = $this->container->get('config.factory')->get('system.module');
     foreach ($modules as $module) {
       unset($module_filenames[$module]);
+      $system_config->clear('enabled.' . $module);
     }
+    $system_config->save();
     $module_handler->setModuleList($module_filenames);
     $module_handler->resetImplementations();
     // Update the kernel to remove their services.
only in patch2:
unchanged:
--- a/core/modules/field/lib/Drupal/field/Tests/FieldInfoTest.php
+++ b/core/modules/field/lib/Drupal/field/Tests/FieldInfoTest.php
@@ -173,6 +173,11 @@ function testInstancePrepare() {
    * Test that instances on disabled entity types are filtered out.
    */
   function testInstanceDisabledEntityType() {
+    // Disabling the comment module invokes user_modules_uninstalled() and calls
+    // drupal_flush_all_caches(). Install the necessary schema to support this.
+    $this->installSchema('user', array('users_data'));
+    $this->installSchema('system', array('router'));
+
     // For this test the field type and the entity type must be exposed by
     // different modules.
     $this->enableModules(array('node', 'comment'));
@@ -187,9 +192,10 @@ function testInstanceDisabledEntityType() {
       'entity_type' => 'comment',
       'bundle' => 'comment_node_article',
     );
-    entity_create('field_instance', $instance_definition);
+    entity_create('field_instance', $instance_definition)->save();
 
-    // Disable coment module. This clears field_info cache.
+    $this->assertNotNull(field_info_instance('comment', 'field', 'comment_node_article'), 'Instance is returned on enabled entity types.');
+    // Disable comment module. This clears field_info cache.
     module_uninstall(array('comment'));
     $this->assertNull(field_info_instance('comment', 'field', 'comment_node_article'), 'No instances are returned on disabled entity types.');
   }