implement suggestion for unknown command in console application

suggestion is based on two principles:

- first suggest commands the begin with the unknown name, to suggest
  commands after accidentally hitting enter
- second find similar commands by computing the levenshtein distance
  which is a measurement on how many changes need to be made to convert
  one string into another. This is perfect for finding typos.

tests/framework/console/UnkownCommandExceptionTest.php

@@ -0,0 +1,70 @@
+<?php
+/**
+ * @link http://www.yiiframework.com/
+ * @copyright Copyright (c) 2008 Yii Software LLC
+ * @license http://www.yiiframework.com/license/
+ */
+
+namespace yiiunit\framework\console;
+
+use Yii;
+use yii\console\Application;
+use yii\console\UnknownCommandException;
+use yiiunit\TestCase;
+
+/**
+ * @group console
+ */
+class UnkownCommandExceptionTest extends TestCase
+{
+    public function setUp()
+    {
+        $this->mockApplication([
+            'enableCoreCommands' => false,
+            'controllerMap' => [
+                'cache' => 'yii\console\controllers\CacheController',
+                'migrate' => 'yii\console\controllers\MigrateController',
+                'message' => 'yii\console\controllers\MessageController',
+            ],
+        ]);
+    }
+
+    public function suggestedCommandsProvider()
+    {
+        return [
+            ['migate', ['migrate']],
+            ['mihate/u', ['migrate/up']],
+            ['mirgte/u', ['migrate/up']],
+            ['mirgte/up', ['migrate/up']],
+            ['mirgte', ['migrate']],
+            ['hlp', ['help']],
+            ['ca', ['cache', 'cache/flush', 'cache/flush-all', 'cache/flush-schema', 'cache/index']],
+            ['cach', ['cache', 'cache/flush', 'cache/flush-all', 'cache/flush-schema', 'cache/index']],
+            ['cach/fush', ['cache/flush']],
+            ['cach/fushall', ['cache/flush-all']],
+            ['what?', []],
+            // test UTF 8 chars
+            ['ёлка', []],
+            // this crashes levenshtein because string is longer than 255 chars
+            [str_repeat('asdw1234', 31), []],
+            [str_repeat('asdw1234', 32), []],
+            [str_repeat('asdw1234', 33), []],
+        ];
+    }
+
+    /**
+     * @dataProvider suggestedCommandsProvider
+     */
+    public function testSuggestCommand($command, $expectedSuggestion)
+    {
+        $exception = new UnknownCommandException($command, Yii::$app);
+        $this->assertEquals($expectedSuggestion, $exception->getSuggestedAlternatives());
+    }
+
+    public function testNameAndConstructor()
+    {
+        $exception = new UnknownCommandException('test', Yii::$app);
+        $this->assertEquals('Unknown command', $exception->getName());
+        $this->assertEquals('test', $exception->command);
+    }
+}