Config: display user-friendly message when invalid generator is passed

This commit improves how `Config::processLongArgument()` handles the
`--generator` parameter. Now it will show a user-friendly message if an
invalid generator name is passed. Before, an invalid generator name
caused a fatal error.

src/Config.php

@@ -1233,7 +1233,20 @@ public function processLongArgument($arg, $pos)
                     break;
                 }
 
-                $this->generator = substr($arg, 10);
+                $generatorName   = substr($arg, 10);
+                $validGenerators = [
+                    'Text',
+                    'HTML',
+                    'Markdown',
+                ];
+
+                if (in_array($generatorName, $validGenerators, true) === false) {
+                    $error  = 'ERROR: "'.$generatorName.'" is not a valid generator. Valid options are: Text, HTML, and Markdown.'.PHP_EOL.PHP_EOL;
+                    $error .= $this->printShortUsage(true);
+                    throw new DeepExitException($error, 3);
+                }
+
+                $this->generator = $generatorName;
                 self::$overriddenDefaults['generator'] = true;
             } else if (substr($arg, 0, 9) === 'encoding=') {
                 if (isset(self::$overriddenDefaults['encoding']) === true) {

tests/Core/Config/GeneratorArgTest.php

@@ -25,35 +25,35 @@ final class GeneratorArgTest extends TestCase
      *
      * @param string $generatorName Generator name.
      *
-     * @dataProvider dataGeneratorNames
+     * @dataProvider dataValidGeneratorNames
      *
      * @return void
      */
-    public function testGenerators($generatorName)
+    public function testValidGenerators($generatorName)
     {
         $config = new ConfigDouble(["--generator=$generatorName"]);
 
         $this->assertSame($generatorName, $config->generator);
 
-    }//end testGenerators()
+    }//end testValidGenerators()
 
 
     /**
-     * Data provider for testGenerators().
+     * Data provider for testValidGenerators().
      *
-     * @see self::testGenerators()
+     * @see self::testValidGenerators()
      *
      * @return array<int, array<string>>
      */
-    public static function dataGeneratorNames()
+    public static function dataValidGeneratorNames()
     {
         return [
             ['Text'],
             ['HTML'],
             ['Markdown'],
         ];
 
-    }//end dataGeneratorNames()
+    }//end dataValidGeneratorNames()
 
 
     /**
@@ -76,4 +76,51 @@ public function testOnlySetOnce()
     }//end testOnlySetOnce()
 
 
+    /**
+     * Ensure that an exception is thrown for an invalid generator.
+     *
+     * @param string $generatorName Generator name.
+     *
+     * @dataProvider dataInvalidGeneratorNames
+     *
+     * @return void
+     */
+    public function testInvalidGenerator($generatorName)
+    {
+        $exception = 'PHP_CodeSniffer\Exceptions\DeepExitException';
+        $message   = 'ERROR: "'.$generatorName.'" is not a valid generator. Valid options are: Text, HTML, and Markdown.';
+
+        if (method_exists($this, 'expectException') === true) {
+            // PHPUnit 5+.
+            $this->expectException($exception);
+            $this->expectExceptionMessage($message);
+        } else {
+            // PHPUnit 4.
+            $this->setExpectedException($exception, $message);
+        }
+
+        new ConfigDouble(["--generator={$generatorName}"]);
+
+    }//end testInvalidGenerator()
+
+
+    /**
+     * Data provider for testInvalidGenerator().
+     *
+     * @see self::testInvalidGenerator()
+     *
+     * @return array<int, array<string>>
+     */
+    public static function dataInvalidGeneratorNames()
+    {
+        return [
+            ['InvalidGenerator'],
+            ['Text,HTML'],
+            ['TEXT'],
+            [''],
+        ];
+
+    }//end dataInvalidGeneratorNames()
+
+
 }//end class