diff --git a/tests/Core/AbstractMethodUnitTest.php b/tests/Core/AbstractMethodUnitTest.php
index 4d4f546995..c1725b0cd2 100644
--- a/tests/Core/AbstractMethodUnitTest.php
+++ b/tests/Core/AbstractMethodUnitTest.php
@@ -13,6 +13,7 @@
 use PHP_CodeSniffer\Ruleset;
 use PHP_CodeSniffer\Files\DummyFile;
 use PHPUnit\Framework\TestCase;
+use ReflectionProperty;
 
 abstract class AbstractMethodUnitTest extends TestCase
 {
@@ -45,9 +46,22 @@ abstract class AbstractMethodUnitTest extends TestCase
      */
     public static function setUpBeforeClass()
     {
-        $config            = new Config();
-        $config->standards = ['PSR1'];
+        /*
+         * 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 a usable value to circumvent Config trying to find a phpcs.xml config file.
+        self::setStaticConfigProperty('overriddenDefaults', ['standards' => ['PSR1']]);
+
+        // 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 Config();
         $ruleset = new Ruleset($config);
 
         // Default to a file with the same name as the test class. Extension is property based.
@@ -74,9 +88,33 @@ public static function tearDownAfterClass()
     {
         self::$phpcsFile = null;
 
+        // Reset the static properties in the Config class to their defaults to prevent tests influencing each other.
+        self::setStaticConfigProperty('overriddenDefaults', []);
+        self::setStaticConfigProperty('executablePaths', []);
+        self::setStaticConfigProperty('configData', null);
+        self::setStaticConfigProperty('configDataFile', null);
+
     }//end tearDownAfterClass()
 
 
+    /**
+     * Helper function to set the value of a private static property on the 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);
+        $property->setValue($value);
+        $property->setAccessible(false);
+
+    }//end setStaticConfigProperty()
+
+
     /**
      * Get the token pointer for a target token based on a specific comment found on the line before.
      *