diff --git a/tests/RuleTestCase.php b/tests/RuleTestCase.php
index b9e73d1..c503a67 100644
--- a/tests/RuleTestCase.php
+++ b/tests/RuleTestCase.php
@@ -54,7 +54,7 @@ protected function processActualErrors(array $actualErrors): array
 
         foreach ($actualErrors as $error) {
             $usedLine = $error->getLine() ?? -1;
-            $key = $usedLine . '-' . uniqid();
+            $key = sprintf('%04d', $usedLine) . '-' . uniqid();
             $resultToAssert[$key] = $this->formatErrorForAssert($error->getMessage(), $usedLine);
 
             self::assertNotNull($error->getIdentifier(), "Missing error identifier for error: {$error->getMessage()}");
@@ -88,7 +88,7 @@ private function parseExpectedErrors(string $file): array
 
             foreach ($matches[1] as $error) {
                 $actualLine = $line + 1;
-                $key = $actualLine . '-' . uniqid();
+                $key = sprintf('%04d', $actualLine) . '-' . uniqid();
                 $expectedErrors[$key] = $this->formatErrorForAssert(trim($error), $actualLine);
             }
         }