Forbid backticks operator (#20)

ptscs/ruleset.xml

@@ -20,6 +20,8 @@
         <exclude name="Ptscs.PSR12.FileHeader.SpacingAfterBlock" />
     </rule>
 
+    <rule ref="Generic.PHP.BacktickOperator" />
+
     <!--++++++++++++++++++++++++++++++++++++
     Additional rules
     ++++++++++++++++++++++++++++++++++++-->

tests/Sniffs/Generic/BacktickOperatorTest.php

@@ -0,0 +1,17 @@
+<?php declare(strict_types=1);
+
+namespace Ptscs\Tests\Sniffs\Generic;
+
+use Iterator;
+use Ptscs\Tests\SniffTestCase;
+use Ptscs\Tests\Utils\ErrorData;
+
+final class BacktickOperatorTest extends SniffTestCase
+{
+    public static function provideTestData(): Iterator
+    {
+        yield [
+          [new ErrorData(3, 'Generic.PHP.BacktickOperator.Found')],
+        ];
+    }
+}

tests/Sniffs/Generic/_data/BacktickOperator.php.fixed

@@ -0,0 +1,3 @@
+<?php declare(strict_types=1);
+
+echo `ls -la`;

tests/Sniffs/Generic/_data/BacktickOperator.php.inc

@@ -0,0 +1,3 @@
+<?php declare(strict_types=1);
+
+echo `ls -la`;