Split DateInterval test expectations by PHP version

On PHP < 8.1, DateInterval::__construct() prefixes the exception
message with "DateInterval::__construct(): ", while PHP 8.1+ uses
a shorter format. Gate the existing test with RequiresPhp(>= 8.1.0)
and add a separate testLegacyPhp method for older PHP versions.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: 2 people

tests/PHPStan/Rules/DateIntervalInstantiationRuleTest.php

@@ -3,6 +3,7 @@
 namespace PHPStan\Rules;
 
 use PHPStan\Testing\RuleTestCase;
+use PHPUnit\Framework\Attributes\RequiresPhp;
 
 /**
  * @extends RuleTestCase<DateIntervalInstantiationRule>
@@ -15,6 +16,7 @@ protected function getRule(): Rule
 		return new DateIntervalInstantiationRule();
 	}
 
+	#[RequiresPhp('>= 8.1.0')]
 	public function test(): void
 	{
 		$this->analyse(
@@ -44,4 +46,34 @@ public function test(): void
 		);
 	}
 
+	#[RequiresPhp('< 8.1.0')]
+	public function testLegacyPhp(): void
+	{
+		$this->analyse(
+			[__DIR__ . '/data/date-interval-instantiation.php'],
+			[
+				[
+					'Instantiating DateInterval with 1M produces an error: DateInterval::__construct(): Unknown or bad format (1M)',
+					5,
+				],
+				[
+					'Instantiating DateInterval with asdfasdf produces an error: DateInterval::__construct(): Unknown or bad format (asdfasdf)',
+					18,
+				],
+				[
+					'Instantiating DateInterval with  produces an error: DateInterval::__construct(): Unknown or bad format ()',
+					21,
+				],
+				[
+					'Instantiating DateInterval with 1M produces an error: DateInterval::__construct(): Unknown or bad format (1M)',
+					30,
+				],
+				[
+					'Instantiating DateInterval with invalid produces an error: DateInterval::__construct(): Unknown or bad format (invalid)',
+					37,
+				],
+			],
+		);
+	}
+
 }