Multiplication mutator should not mutate when return value is integer

src/Mutator/Arithmetic/Multiplication.php

@@ -39,6 +39,9 @@
 use Infection\Mutator\GetMutatorName;
 use Infection\Mutator\Mutator;
 use Infection\Mutator\MutatorCategory;
+use Infection\PhpParser\Visitor\ParentConnector;
+use Infection\PhpParser\Visitor\ReflectionVisitor;
+use function is_string;
 use PhpParser\Node;
 
 /**
@@ -94,7 +97,25 @@ public function canMutate(Node $node): bool
             return false;
         }
 
-        return true;
+        $functionScope = $node->getAttribute(ReflectionVisitor::FUNCTION_SCOPE_KEY);
+
+        if (!$functionScope instanceof Node\Stmt\ClassMethod) {
+            return true;
+        }
+
+        $parentNode = ParentConnector::getParent($node);
+
+        if (!$parentNode instanceof Node\Stmt\Return_) {
+            return true;
+        }
+
+        $returnType = $functionScope->getReturnType();
+
+        if ($returnType instanceof Node\Identifier) {
+            $returnType = $returnType->name;
+        }
+
+        return !(is_string($returnType) && $returnType === 'int');
     }
 
     private function isNumericOne(Node $node): bool

tests/phpunit/Mutator/Arithmetic/MultiplicationTest.php

@@ -135,6 +135,48 @@ public function mutationsProvider(): iterable
 <?php
 
 $a = $b * -1.0;
+PHP
+        ];
+
+        yield 'It does not mutate when class method returns type is integer' => [
+            <<<'PHP'
+<?php
+
+new class
+{
+    public function mul(int $a, int $b): int
+    {
+        return $a * $b;
+    }
+};
+PHP
+        ];
+
+        yield 'It mutates when class method returns type is integer' => [
+            <<<'PHP'
+<?php
+
+new class
+{
+    public function mul(int $a, int $b): int
+    {
+        $c = $a * $b;
+
+        return 1;
+    }
+};
+PHP,
+            <<<'PHP'
+<?php
+
+new class
+{
+    public function mul(int $a, int $b) : int
+    {
+        $c = $a / $b;
+        return 1;
+    }
+};
 PHP
         ];
     }