Add test for GMP increment/decrement operations

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: 2 people

tests/PHPStan/Rules/Operators/InvalidIncDecOperationRuleTest.php

@@ -249,4 +249,9 @@ public function testBcMathNumber(): void
 		$this->analyse([__DIR__ . '/data/inc-dec-bcmath-number.php'], []);
 	}
 
+	public function testGmp(): void
+	{
+		$this->analyse([__DIR__ . '/data/inc-dec-gmp.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Operators/data/inc-dec-gmp.php

@@ -0,0 +1,21 @@
+<?php
+
+namespace IncDecGmp;
+
+use GMP;
+
+function testPreInc(GMP $x): void {
+	++$x;
+}
+
+function testPostInc(GMP $x): void {
+	$x++;
+}
+
+function testPreDec(GMP $x): void {
+	--$x;
+}
+
+function testPostDec(GMP $x): void {
+	$x--;
+}