Tests: introduce AbstractRunnerTestCase base class

... for tests which directly invoke the `Runner` class.

Author: jrfnl

tests/Core/Runner/AbstractRunnerTestCase.php

@@ -0,0 +1,93 @@
+<?php
+/**
+ * Base class to use for tests invoking the Runner class.
+ *
+ * As those tests will use the _real_ Config class instead of the ConfigDouble, we need to ensure
+ * this doesn't negatively impact other tests, what with the Config using static properties.
+ *
+ * @copyright 2025 PHPCSStandards and contributors
+ * @license   https://github.com/PHPCSStandards/PHP_CodeSniffer/blob/master/licence.txt BSD Licence
+ */
+
+namespace PHP_CodeSniffer\Tests\Core\Runner;
+
+use PHPUnit\Framework\TestCase;
+use ReflectionProperty;
+
+abstract class AbstractRunnerTestCase extends TestCase
+{
+
+
+    /**
+     * Set static properties in the Config class to prevent tests influencing each other.
+     *
+     * @before
+     *
+     * @return void
+     */
+    public function setConfigStatics()
+    {
+        // Set to the property's default value to clear out potentially set values from other tests.
+        self::setStaticConfigProperty('overriddenDefaults', []);
+        self::setStaticConfigProperty('executablePaths', []);
+
+        // Set to values which prevent the test-runner user's `CodeSniffer.conf` file
+        // from being read and influencing the tests.
+        self::setStaticConfigProperty('configData', []);
+        self::setStaticConfigProperty('configDataFile', '');
+
+    }//end setConfigStatics()
+
+
+    /**
+     * Clean up after each finished test.
+     *
+     * @after
+     *
+     * @return void
+     */
+    public function clearArgv()
+    {
+        $_SERVER['argv'] = [];
+
+    }//end clearArgv()
+
+
+    /**
+     * Reset the static properties in the Config class to their true defaults to prevent this class
+     * from influencing other tests.
+     *
+     * @afterClass
+     *
+     * @return void
+     */
+    public static function reset()
+    {
+        self::setStaticConfigProperty('overriddenDefaults', []);
+        self::setStaticConfigProperty('executablePaths', []);
+        self::setStaticConfigProperty('configData', null);
+        self::setStaticConfigProperty('configDataFile', null);
+        $_SERVER['argv'] = [];
+
+    }//end reset()
+
+
+    /**
+     * Helper function to set a 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(null, $value);
+        $property->setAccessible(false);
+
+    }//end setStaticConfigProperty()
+
+
+}//end class