diff -u b/core/modules/file/src/Plugin/migrate/destination/EntityFile.php b/core/modules/file/src/Plugin/migrate/destination/EntityFile.php
--- b/core/modules/file/src/Plugin/migrate/destination/EntityFile.php
+++ b/core/modules/file/src/Plugin/migrate/destination/EntityFile.php
@@ -3,11 +3,7 @@
 namespace Drupal\file\Plugin\migrate\destination;
 
 use Drupal\Component\Utility\Unicode;
-use Drupal\Core\Entity\EntityManagerInterface;
-use Drupal\Core\Entity\EntityStorageInterface;
-use Drupal\Core\Field\FieldTypePluginManagerInterface;
 use Drupal\Core\Field\Plugin\Field\FieldType\UriItem;
-use Drupal\migrate\Plugin\MigrationInterface;
 use Drupal\migrate\Row;
 use Drupal\migrate\MigrateException;
 use Drupal\migrate\Plugin\migrate\destination\EntityContentBase;
@@ -32,6 +28,9 @@
     // By default the entity key (fid) would be used, but we want to make sure
     // we're loading the matching URI.
     $destination = $row->getDestinationProperty('uri');
+    if (empty($destination)) {
+      throw new MigrateException('Destination property uri not provided');
+    }
     $entity = $this->storage->loadByProperties(['uri' => $destination]);
     if ($entity) {
       return reset($entity);
diff -u b/core/modules/file/tests/src/Kernel/Migrate/d6/FileMigrationTestTrait.php b/core/modules/file/tests/src/Kernel/Migrate/d6/FileMigrationTestTrait.php
--- b/core/modules/file/tests/src/Kernel/Migrate/d6/FileMigrationTestTrait.php
+++ b/core/modules/file/tests/src/Kernel/Migrate/d6/FileMigrationTestTrait.php
@@ -21,7 +21,7 @@
   /**
    * {@inheritdoc}
    */
-  protected function processMigration(MigrationInterface $migration) {
+  protected function prepareMigration(MigrationInterface $migration) {
     // File migrations need a source_base_path.
     // @see MigrateUpgradeRunBatch::run
     $destination = $migration->getDestinationConfiguration();
reverted:
--- b/core/modules/file/tests/src/Unit/Plugin/migrate/process/UrlEncodeTest.php
+++ /dev/null
@@ -1,65 +0,0 @@
-<?php
-
-namespace Drupal\Tests\file\Unit\Plugin\migrate\process;
-
-use Drupal\migrate\Plugin\migrate\process\UrlEncode;
-use Drupal\migrate\MigrateExecutable;
-use Drupal\migrate\MigrateMessage;
-use Drupal\migrate\Row;
-use Drupal\Tests\migrate\Unit\MigrateTestCase;
-
-/**
- * @coversDefaultClass \Drupal\migrate\Plugin\migrate\process\UrlEncode
- * @group file
- */
-class UrlEncodeTest extends MigrateTestCase {
-
-  /**
-   * @inheritdoc
-   */
-  protected $migrationConfiguration = [
-    'id' => 'test',
-  ];
-
-  /**
-   * The data provider for testing URL encoding scenarios.
-   *
-   * @return array
-   *   An array of URLs to test.
-   */
-  public function urlDataProvider() {
-    return [
-      'A URL with no characters requiring encoding' => ['http://example.com/normal_url.html', 'http://example.com/normal_url.html'],
-      'The definitive use case - encoding spaces in URLs' => ['http://example.com/url with spaces.html', 'http://example.com/url%20with%20spaces.html'],
-      'Local filespecs without spaces should not be transformed' => ['/tmp/normal.txt', '/tmp/normal.txt'],
-      'Local filespecs with spaces should not be transformed' => ['/tmp/with spaces.txt', '/tmp/with spaces.txt'],
-      'Make sure URL characters (:, ?, &) are not encoded but others are.' => ['https://example.com/?a=b@c&d=e+f%', 'https://example.com/?a%3Db%40c&d%3De%2Bf%25'],
-    ];
-  }
-
-  /**
-   * Cover various encoding scenarios.
-   * @dataProvider urlDataProvider
-   */
-  public function testUrls($input, $output) {
-    $this->assertEquals($output, $this->doTransform($input));
-  }
-
-  /**
-   * Perform the urlencode process plugin over the given value.
-   *
-   * @param string $value
-   *   URL to be encoded.
-   *
-   * @return string
-   *   Encoded URL.
-   */
-  protected function doTransform($value) {
-    $executable = new MigrateExecutable($this->getMigration(), new MigrateMessage());
-    $row = new Row([], []);
-
-    return (new UrlEncode([], 'urlencode', []))
-      ->transform($value, $executable, $row, 'foobaz');
-  }
-
-}
diff -u b/core/modules/migrate/src/Plugin/migrate/process/FileCopy.php b/core/modules/migrate/src/Plugin/migrate/process/FileCopy.php
--- b/core/modules/migrate/src/Plugin/migrate/process/FileCopy.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/FileCopy.php
@@ -76,7 +76,7 @@
    * {@inheritdoc}
    */
   public function transform($value, MigrateExecutableInterface $migrate_executable, Row $row, $destination_property) {
-    // If we're stubbing a file entity, return a uri of NULL so it will get
+    // If we're stubbing a file entity, return a URI of NULL so it will get
     // stubbed by the general process.
     if ($row->isStub()) {
       return NULL;
@@ -94,13 +94,14 @@
     }
 
     $replace = $this->getOverwriteMode();
-    // We attempt the copy/move first to avoid calling file_prepare_directory() any
-    // more than absolutely necessary.
+    // We attempt the copy/move first to avoid calling file_prepare_directory()
+    // any more than absolutely necessary.
     $final_destination = $this->writeFile($source, $destination, $replace);
     if ($final_destination) {
       return $final_destination;
     }
-    // If writeFile didn't work, make sure there's a writable directory in place.
+    // If writeFile didn't work, make sure there's a writable directory in
+    // place.
     $dir = $this->getDirectory($destination);
     if (!file_prepare_directory($dir, FILE_CREATE_DIRECTORY | FILE_MODIFY_PERMISSIONS)) {
       throw new MigrateException("Could not create or write to directory '$dir'");
diff -u b/core/modules/migrate/src/Plugin/migrate/process/UrlEncode.php b/core/modules/migrate/src/Plugin/migrate/process/UrlEncode.php
--- b/core/modules/migrate/src/Plugin/migrate/process/UrlEncode.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/UrlEncode.php
@@ -52,7 +52,7 @@
           $parsed_url[$parsed_url_key] = $urlencoded_parsed_url_value;
         }
       }
-      $value = (string)Uri::fromParts($parsed_url);
+      $value = (string) Uri::fromParts($parsed_url);
     }
     return $value;
   }
diff -u b/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php b/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php
--- b/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php
+++ b/core/modules/migrate/tests/src/Kernel/MigrateTestBase.php
@@ -144,7 +144,7 @@
    * @param \Drupal\migrate\Plugin\MigrationInterface $migration
    *   The migration to execute.
    */
-  protected function processMigration(MigrationInterface $migration) {
+  protected function prepareMigration(MigrationInterface $migration) {
     // Default implementation for test classes not requiring modification.
   }
 
@@ -165,7 +165,7 @@
       static::migrateDumpAlter($this);
     }
 
-    $this->processMigration($this->migration);
+    $this->prepareMigration($this->migration);
     (new MigrateExecutable($this->migration, $this))->import();
   }
 
diff -u b/core/modules/migrate/tests/src/Unit/process/CopyFileTest.php b/core/modules/migrate/tests/src/Unit/process/CopyFileTest.php
--- b/core/modules/migrate/tests/src/Unit/process/CopyFileTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/CopyFileTest.php
@@ -22,7 +22,9 @@
   public static $modules = ['system'];
 
   /**
-   * @var FileSystemInterface
+   * The file system service.
+   *
+   * @var \Drupal\Core\File\FileSystemInterface
    */
   protected $fileSystem;