diff --git a/tests/lib/AppConfigTest.php b/tests/lib/AppConfigTest.php
new file mode 100644
index 00000000000..d7358c4a1e9
--- /dev/null
+++ b/tests/lib/AppConfigTest.php
@@ -0,0 +1,201 @@
+<?php
+
+declare(strict_types=1);
+/**
+ * SPDX-FileCopyrightText: 2025 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+namespace Test;
+
+use OC\AppConfig;
+use OC\Config\ConfigManager;
+use OC\Config\PresetManager;
+use OCP\DB\IResult;
+use OCP\DB\QueryBuilder\IExpressionBuilder;
+use OCP\DB\QueryBuilder\IQueryBuilder;
+use OCP\ICache;
+use OCP\ICacheFactory;
+use OCP\IConfig;
+use OCP\IDBConnection;
+use OCP\Security\ICrypto;
+use PHPUnit\Framework\MockObject\MockObject;
+use Psr\Log\LoggerInterface;
+
+/**
+ * Class AppConfigTest
+ *
+ * @package Test
+ */
+class AppConfigTest extends TestCase {
+	private IConfig&MockObject $config;
+	private IDBConnection&MockObject $connection;
+	private ConfigManager&MockObject $configManager;
+	private PresetManager&MockObject $presetManager;
+	private LoggerInterface&MockObject $logger;
+	private ICrypto&MockObject $crypto;
+	private ICacheFactory&MockObject $cacheFactory;
+	private ICache&MockObject $localCache;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		$this->connection = $this->createMock(IDBConnection::class);
+		$this->config = $this->createMock(IConfig::class);
+		$this->configManager = $this->createMock(ConfigManager::class);
+		$this->presetManager = $this->createMock(PresetManager::class);
+		$this->logger = $this->createMock(LoggerInterface::class);
+		$this->crypto = $this->createMock(ICrypto::class);
+		$this->cacheFactory = $this->createMock(ICacheFactory::class);
+		$this->localCache = $this->createMock(ICache::class);
+	}
+
+	protected function getAppConfig($cached = false): AppConfig {
+		$this->config->method('getSystemValueBool')
+			->with('cache_app_config', $cached)
+			->willReturn(true);
+		$this->cacheFactory->method('isLocalCacheAvailable')->willReturn($cached);
+		if ($cached) {
+			$this->cacheFactory->method('createLocal')->willReturn($this->localCache);
+		}
+
+		return new AppConfig(
+			$this->connection,
+			$this->config,
+			$this->configManager,
+			$this->presetManager,
+			$this->logger,
+			$this->crypto,
+			$this->cacheFactory,
+		);
+	}
+
+	public function testCachedRead(): void {
+		$this->localCache->expects(self::once())
+			->method('get')
+			->with('OC\\AppConfig')
+			->willReturn([
+				'fastCache' => [
+					'appid' => [
+						'some-key' => 'some-value',
+						'other-key' => 'other value'
+					],
+				],
+				'valueTypes' => [
+					'appid' => [
+						'some-key' => AppConfig::VALUE_STRING,
+						'other-key' => AppConfig::VALUE_STRING,
+					],
+				],
+			]);
+
+		$this->connection->expects(self::never())->method('getQueryBuilder');
+		$config = $this->getAppConfig(true);
+
+
+		$this->assertSame('some-value', $config->getValueString('appid', 'some-key'));
+		$this->assertSame('other value', $config->getValueString('appid', 'other-key'));
+		$this->assertSame(AppConfig::VALUE_STRING, $config->getValueType('appid', 'some-key', false));
+	}
+
+	public function testCachedLazyRead(): void {
+		$this->localCache->expects(self::once())
+			->method('get')
+			->with('OC\\AppConfig')
+			->willReturn([
+				'fastCache' => [
+					'appid' => [
+						'fast-key' => 'fast value',
+					],
+				],
+				'lazyCache' => [
+					'appid' => [
+						'lazy-key' => 'lazy value',
+					],
+				],
+				'valueTypes' => [
+					'appid' => [
+						'some-key' => AppConfig::VALUE_STRING,
+						'lazy-key' => AppConfig::VALUE_STRING,
+					],
+				],
+			]);
+
+		$this->connection->expects(self::never())->method('getQueryBuilder');
+		$config = $this->getAppConfig(true);
+
+
+		$this->assertSame('fast value', $config->getValueString('appid', 'fast-key'));
+		$this->assertSame('lazy value', $config->getValueString('appid', 'lazy-key', '', true));
+	}
+
+	public function testOnlyFastKeyCached(): void {
+		$this->localCache->expects(self::atLeastOnce())
+			->method('get')
+			->with('OC\\AppConfig')
+			->willReturn([
+				'fastCache' => [
+					'appid' => [
+						'fast-key' => 'fast value',
+					],
+				],
+				'valueTypes' => [
+					'appid' => [
+						'fast-key' => AppConfig::VALUE_STRING,
+					],
+				],
+			]);
+
+		$result = $this->createMock(IResult::class);
+		$result->method('fetchAll')->willReturn([
+			['lazy' => 1, 'appid' => 'appid', 'configkey' => 'lazy-key', 'configvalue' => 'lazy value'],
+		]);
+		$expression = $this->createMock(IExpressionBuilder::class);
+		$queryBuilder = $this->createMock(IQueryBuilder::class);
+		$queryBuilder->method('from')->willReturn($queryBuilder);
+		$queryBuilder->method('expr')->willReturn($expression);
+		$queryBuilder->method('executeQuery')->willReturn($result);
+
+		$this->connection->expects(self::once())->method('getQueryBuilder')->willReturn($queryBuilder);
+		$config = $this->getAppConfig(true);
+
+
+		$this->assertSame('fast value', $config->getValueString('appid', 'fast-key'));
+		$this->assertSame('lazy value', $config->getValueString('appid', 'lazy-key', '', true));
+	}
+
+	public function testWritesAreCached(): void {
+		$this->localCache->expects(self::atLeastOnce())
+			->method('get')
+			->with('OC\\AppConfig')
+			->willReturn([
+				'fastCache' => [
+					'appid' => [
+						'first-key' => 'first value',
+					],
+				],
+				'valueTypes' => [
+					'appid' => [
+						'first-key' => AppConfig::VALUE_STRING,
+					],
+				],
+			]);
+
+		$expression = $this->createMock(IExpressionBuilder::class);
+		$queryBuilder = $this->createMock(IQueryBuilder::class);
+		$queryBuilder->expects(self::once())
+			->method('update')
+			->with('appconfig', null)
+			->willReturn($queryBuilder);
+		$queryBuilder->method('set')->willReturn($queryBuilder);
+		$queryBuilder->method('where')->willReturn($queryBuilder);
+		$queryBuilder->method('andWhere')->willReturn($queryBuilder);
+		$queryBuilder->method('expr')->willReturn($expression);
+		$this->connection->expects(self::once())->method('getQueryBuilder')->willReturn($queryBuilder);
+
+		$config = $this->getAppConfig(true);
+
+		$this->assertSame('first value', $config->getValueString('appid', 'first-key'));
+		$config->setValueString('appid', 'first-key', 'new value');
+		$this->assertSame('new value', $config->getValueString('appid', 'first-key'));
+	}
+}