function DirectoryTest::testFileDestination
Tests the destination file path.
This will test the filepath for a destination based on passed flags and whether or not the file exists.
If a file exists, ::getDestinationFilename($destination, $replace) will either return:
- the existing filepath, if $replace is FileSystemInterface::EXISTS_REPLACE
 - a new filepath if FileSystemInterface::EXISTS_RENAME
 - an error (returning FALSE) if FileSystemInterface::EXISTS_ERROR.
 
If the file doesn't currently exist, then it will simply return the filepath.
File
- 
              core/
tests/ Drupal/ KernelTests/ Core/ File/ DirectoryTest.php, line 153  
Class
- DirectoryTest
 - Tests operations dealing with directories.
 
Namespace
Drupal\KernelTests\Core\FileCode
public function testFileDestination() {
  // First test for non-existent file.
  $destination = 'core/misc/xyz.txt';
  /** @var \Drupal\Core\File\FileSystemInterface $file_system */
  $file_system = \Drupal::service('file_system');
  $path = $file_system->getDestinationFilename($destination, FileSystemInterface::EXISTS_REPLACE);
  $this->assertEquals($destination, $path, 'Non-existing filepath destination is correct with FileSystemInterface::EXISTS_REPLACE.');
  $path = $file_system->getDestinationFilename($destination, FileSystemInterface::EXISTS_RENAME);
  $this->assertEquals($destination, $path, 'Non-existing filepath destination is correct with FileSystemInterface::EXISTS_RENAME.');
  $path = $file_system->getDestinationFilename($destination, FileSystemInterface::EXISTS_ERROR);
  $this->assertEquals($destination, $path, 'Non-existing filepath destination is correct with FileSystemInterface::EXISTS_ERROR.');
  $destination = 'core/misc/druplicon.png';
  $path = $file_system->getDestinationFilename($destination, FileSystemInterface::EXISTS_REPLACE);
  $this->assertEquals($destination, $path, 'Existing filepath destination remains the same with FileSystemInterface::EXISTS_REPLACE.');
  $path = $file_system->getDestinationFilename($destination, FileSystemInterface::EXISTS_RENAME);
  $this->assertNotEquals($destination, $path, 'A new filepath destination is created when filepath destination already exists with FileSystemInterface::EXISTS_RENAME.');
  $path = $file_system->getDestinationFilename($destination, FileSystemInterface::EXISTS_ERROR);
  $this->assertFalse($path, 'An error is returned when filepath destination already exists with FileSystemInterface::EXISTS_ERROR.');
  // Invalid UTF-8 causes an exception.
  $this->expectException(FileException::class);
  $this->expectExceptionMessage("Invalid filename 'a\xfftest\x80€.txt'");
  $file_system->getDestinationFilename("core/misc/a\xfftest\x80€.txt", FileSystemInterface::EXISTS_REPLACE);
}
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