improved error message if user doesn't exists

lib/private/encryption/decryptall.php

@@ -80,6 +80,11 @@ class DecryptAll {
 		$this->input = $input;
 		$this->output = $output;
 
+		if ($user !== '' && $this->userManager->userExists($user) === false) {
+			$this->output->writeln('User "' . $user . '" does not exist. Please check the username and try again');
+			return false;
+		}
+
 		$this->output->writeln('prepare encryption modules...');
 		if ($this->prepareEncryptionModules($user) === false) {
 			return false;

tests/lib/encryption/decryptalltest.php

@@ -80,11 +80,13 @@ class DecryptAllTest extends TestCase {
 
 	/**
 	 * @dataProvider dataTrueFalse
+	 * @param bool $prepareResult
 	 */
 	public function testDecryptAll($prepareResult) {
 
 		$user = 'user1';
 
+		$this->userManager->expects($this->once())->method('userExists')->willReturn(true);
 		/** @var DecryptAll | \PHPUnit_Framework_MockObject_MockObject |  $instance */
 		$instance = $this->getMockBuilder('OC\Encryption\DecryptAll')
 			->setConstructorArgs(
@@ -120,6 +122,19 @@ class DecryptAllTest extends TestCase {
 		];
 	}
 
+	/**
+	 * test decrypt all call with a user who doesn't exists
+	 */
+	public function testDecryptAllWrongUser() {
+		$this->userManager->expects($this->once())->method('userExists')->willReturn(false);
+		$this->outputInterface->expects($this->once())->method('writeln')
+			->with('User "user1" does not exist. Please check the username and try again');
+
+		$this->assertFalse(
+			$this->instance->decryptAll($this->inputInterface, $this->outputInterface, 'user1')
+		);
+	}
+
 	/**
 	 * @dataProvider dataTrueFalse
 	 */