diff --git a/tests/IntegrationTest/PreexistingPHPCSConfigTest.php b/tests/IntegrationTest/PreexistingPHPCSConfigTest.php
new file mode 100644
index 00000000..288abc3f
--- /dev/null
+++ b/tests/IntegrationTest/PreexistingPHPCSConfigTest.php
@@ -0,0 +1,182 @@
+<?php
+
+/**
+ * This file is part of the Dealerdirect PHP_CodeSniffer Standards
+ * Composer Installer Plugin package.
+ *
+ * @copyright 2022 PHPCodeSniffer Composer Installer Contributors
+ * @license MIT
+ */
+
+namespace Dealerdirect\Composer\Plugin\Installers\PHPCodeSniffer\Tests\IntegrationTest;
+
+use Dealerdirect\Composer\Plugin\Installers\PHPCodeSniffer\Tests\PHPCSVersions;
+use Dealerdirect\Composer\Plugin\Installers\PHPCodeSniffer\Tests\TestCase;
+
+/**
+ * Test correctly handling a pre-existing PHPCS configuration file.
+ *
+ * These tests verify:
+ * - That the plugin will add the `installed_paths` setting correctly.
+ * - That the plugin does not remove or alter existing configurations, except for the `installed_paths`.
+ *
+ * As PHPCS behaves the same whether installed locally or globally, it is unnecessary to run the tests
+ * in both type of environments.
+ *
+ * Note: it is necessary to run against multiple PHPCS versions however, as the output returned
+ * by the `--config-show` command has changed across versions and we need to make sure that
+ * the plugin handles this correctly in all supported PHPCS versions.
+ *
+ * @link https://github.com/PHPCSStandards/composer-installer/pull/98
+ * @link https://github.com/squizlabs/PHP_CodeSniffer/wiki/Configuration-Options
+ */
+final class PreexistingPHPCSConfigTest extends TestCase
+{
+    private $composerConfig = array(
+        'name'        => 'phpcs-composer-installer/preexisting-config-test',
+        'require-dev' => array(
+            'squizlabs/php_codesniffer'                      => null,
+            'dealerdirect/phpcodesniffer-composer-installer' => '*',
+        ),
+    );
+
+    /**
+     * Set up test environment before each test.
+     */
+    protected function set_up()
+    {
+        $this->createTestEnvironment();
+    }
+
+    /**
+     * Clean up after each test.
+     */
+    protected function tear_down()
+    {
+        $this->removeTestEnvironment();
+    }
+
+    /**
+     * Test correctly handling a pre-existing PHPCS configuration file (which doesn't involve
+     * a pre-existing `installed_paths` setting).
+     *
+     * @dataProvider dataPHPCSVersions
+     *
+     * @param string $phpcsVersion  PHPCS version to use in this test.
+     *                              This version is randomly selected from the PHPCS versions compatible
+     *                              with the PHP version used in the test.
+     *
+     * @return void
+     */
+    public function testPreexistingNonInstalledPathsConfigIsKeptIntact($phpcsVersion)
+    {
+        $config = $this->composerConfig;
+        $config['require-dev']['squizlabs/php_codesniffer'] = $phpcsVersion;
+
+        $this->writeComposerJsonFile($config, static::$tempLocalPath);
+
+        /*
+         * 1. Install PHPCS and the plugin.
+         */
+        $this->assertExecute(
+            sprintf('composer install -v --working-dir=%s', escapeshellarg(static::$tempLocalPath)),
+            0,    // Expected exit code.
+            null, // No stdout expectation.
+            null, // No stderr expectation.
+            'Failed to install PHPCS.'
+        );
+
+        // Verify the CodeSniffer.conf file does not exist to start with.
+        $this->assertFileDoesNotExist(
+            static::$tempLocalPath . '/vendor/squizlabs/php_codesniffer/CodeSniffer.conf'
+        );
+
+        // Verify that the config is empty to start with.
+        $result = $this->executeCliCommand('"vendor/bin/phpcs" --config-show', static::$tempLocalPath);
+        $this->assertSame(0, $result['exitcode'], 'Exitcode for "phpcs --config-show" did not match 0 (first run)');
+        $this->assertMatchesRegularExpression(
+            '`^\s*(Using config file:)?\s*$`',
+            $result['stdout'],
+            'PHPCS configuration is not empty to start with.'
+        );
+
+        /*
+         * 2. Set some configs and verify they are registered correctly.
+         *
+         * Note: PHPCS will "show" the config settings in alphabetic order.
+         * These settings have been chosen to ensure there will be settings to show
+         * both before *and* after the `installed_paths` setting.
+         */
+        $command    = '"vendor/bin/phpcs" --config-set %s %s';
+        $failureMsg = 'Exitcode for "phpcs --config-set %s %s" did not match 0';
+        $settings   = array(
+            'default_standard' => 'PSR12',
+            'colors'           => '1',
+            'show_progress'    => '1',
+        );
+
+        foreach ($settings as $name => $value) {
+            $result = $this->executeCliCommand(sprintf($command, $name, $value), static::$tempLocalPath);
+            $this->assertSame(0, $result['exitcode'], sprintf($failureMsg, $name, $value));
+        }
+
+        // Make sure the CodeSniffer.conf file has been created.
+        $this->assertFileExists(
+            static::$tempLocalPath . '/vendor/squizlabs/php_codesniffer/CodeSniffer.conf'
+        );
+
+        // Verify that the config contains the newly set values.
+        $result = $this->executeCliCommand('"vendor/bin/phpcs" --config-show', static::$tempLocalPath);
+        $this->assertSame(0, $result['exitcode'], 'Exitcode for "phpcs --config-show" did not match 0 (second run)');
+
+        $regex = '`colors:\s+1\s+'
+            . 'default_standard:\s+PSR12\s+'
+            . 'show_progress:\s+1\s*$`';
+        $this->assertMatchesRegularExpression(
+            $regex,
+            $result['stdout'],
+            'PHPCS configuration does not show the newly set values correctly.'
+        );
+
+        /*
+         * 3. Install an external standard.
+         */
+        $command = sprintf(
+            'composer require --dev phpcs-composer-installer/dummy-subdir --no-ansi -v --working-dir=%s',
+            escapeshellarg(static::$tempLocalPath)
+        );
+        $this->assertExecute(
+            $command,
+            0,    // Expected exit code.
+            'PHP CodeSniffer Config installed_paths set to ', // Expectation for stdout.
+            null, // No stderr expectation.
+            'Failed to install Dummy subdir standard.'
+        );
+
+        // Verify that the originally set configs are retained and the standard is registered correctly.
+        $result = $this->executeCliCommand('"vendor/bin/phpcs" --config-show', static::$tempLocalPath);
+        $this->assertSame(0, $result['exitcode'], 'Exitcode for "phpcs --config-show" did not match 0 (third run)');
+
+        $regex = '`colors:\s+1\s+'
+            . 'default_standard:\s+PSR12\s+'
+            . 'installed_paths:\s+[^\n\r]+/phpcs-composer-installer/dummy-subdir\s+'
+            . 'show_progress:\s+1\s*$`';
+        $this->assertMatchesRegularExpression(
+            $regex,
+            $result['stdout'],
+            'PHPCS configuration has not been retained and/or updated correctly.'
+        );
+    }
+
+    /**
+     * Data provider.
+     *
+     * @return array
+     */
+    public function dataPHPCSVersions()
+    {
+        // Test against the highest and lowest supported PHPCS version for each major + `master` + PHPCS 4.x dev.
+        $versions = PHPCSVersions::getHighLowEachMajor(true, true);
+        return PHPCSVersions::toDataprovider($versions);
+    }
+}