Reject invalid separator

src/Parser.php

@@ -10,6 +10,7 @@
 namespace SebastianBergmann\CsvParser;
 
 use function is_array;
+use function strlen;
 use Generator;
 use RuntimeException;
 use SplFileObject;
@@ -42,8 +43,15 @@ public function parse(string $filename, Schema $schema): Generator
         return $this->generator($file, $schema);
     }
 
+    /**
+     * @throws InvalidSeparatorException
+     */
     public function setSeparator(string $separator): void
     {
+        if (strlen($separator) !== 1) {
+            throw new InvalidSeparatorException;
+        }
+
         $this->separator = $separator;
     }
 

src/exception/InvalidSeparatorException.php

@@ -0,0 +1,20 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of sebastian/csv-parser.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace SebastianBergmann\CsvParser;
+
+use InvalidArgumentException;
+
+final class InvalidSeparatorException extends InvalidArgumentException implements Exception
+{
+    public function __construct()
+    {
+        parent::__construct('Separator must be a one single-byte character');
+    }
+}

tests/unit/ParserTest.php

@@ -17,6 +17,7 @@
 use PHPUnit\Framework\TestCase;
 
 #[CoversClass(Parser::class)]
+#[CoversClass(InvalidSeparatorException::class)]
 #[UsesClass(Schema::class)]
 #[UsesClass(ColumnDefinition::class)]
 #[UsesClass(Type::class)]
@@ -156,4 +157,14 @@ public function test_Cannot_read_from_CSV_file_that_does_not_exist(): void
 
         (new Parser)->parse('does_not_exist.csv', Schema::from());
     }
+
+    public function testRejectsInvalidSeparator(): void
+    {
+        $parser = new Parser;
+
+        $this->expectException(InvalidSeparatorException::class);
+        $this->expectExceptionMessage('Separator must be a one single-byte character');
+
+        $parser->setSeparator('..');
+    }
 }