diff --git a/PHPCSUtils/TestUtils/UtilityMethodTestCase.php b/PHPCSUtils/TestUtils/UtilityMethodTestCase.php
index 20780dc4..2de11a2d 100644
--- a/PHPCSUtils/TestUtils/UtilityMethodTestCase.php
+++ b/PHPCSUtils/TestUtils/UtilityMethodTestCase.php
@@ -18,6 +18,7 @@
 use PHPCSUtils\Exceptions\TestTargetNotFound;
 use PHPUnit\Framework\TestCase;
 use ReflectionClass;
+use ReflectionProperty;
 
 /**
  * Base class for use when testing utility methods for PHP_CodeSniffer.
@@ -208,9 +209,22 @@ public static function setUpTestFile()
 
         $contents = \file_get_contents($caseFile);
 
+        /*
+         * Set the static properties in the Config class to specific values for performance
+         * and to clear out values from other tests.
+         */
+        self::setStaticConfigProperty('executablePaths', []);
+
+        // Set to values which prevent the test-runner user's `CodeSniffer.conf` file
+        // from being read and influencing the tests. Also prevent an `exec()` call to stty.
+        self::setStaticConfigProperty('configData', ['report_width' => 80]);
+        self::setStaticConfigProperty('configDataFile', '');
+
         $config = new \PHP_CodeSniffer\Config();
 
         /*
+         * Set to a usable value to circumvent Config trying to find a phpcs.xml config file.
+         *
          * We just need to provide a standard so PHPCS will tokenize the file.
          * The standard itself doesn't actually matter for testing utility methods,
          * so use the smallest one to get the fastest results.
@@ -298,6 +312,27 @@ public static function resetTestFile()
         self::$tabWidth      = 4;
         self::$phpcsFile     = null;
         self::$selectedSniff = ['Dummy.Dummy.Dummy'];
+
+        // Reset the static properties in the Config class to their defaults to prevent tests influencing each other.
+        self::setStaticConfigProperty('executablePaths', []);
+        self::setStaticConfigProperty('configData', null);
+        self::setStaticConfigProperty('configDataFile', null);
+    }
+
+    /**
+     * Helper function to set the value of a private static property on the PHPCS Config class.
+     *
+     * @param string $name  The name of the property to set.
+     * @param mixed  $value The value to set the property to.
+     *
+     * @return void
+     */
+    public static function setStaticConfigProperty($name, $value)
+    {
+        $property = new ReflectionProperty('PHP_CodeSniffer\Config', $name);
+        $property->setAccessible(true);
+        $property->setValue(null, $value);
+        $property->setAccessible(false);
     }
 
     /**