diff --git a/tests/session/RedisSessionHandlerTest.php b/tests/session/RedisSessionHandlerTest.php
index 52101ee..78640fd 100644
--- a/tests/session/RedisSessionHandlerTest.php
+++ b/tests/session/RedisSessionHandlerTest.php
@@ -6,6 +6,7 @@
 
 use FastD\Http\Session\Handler\RedisSessionHandler;
 use PHPUnit\Framework\Attributes\AllowMockObjectsWithoutExpectations;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use Redis;
 
@@ -85,4 +86,124 @@ public function testGcIsNoopBecauseRedisExpiresKeys(): void
     {
         $this->assertSame(0, (new RedisSessionHandler($this->createMock(Redis::class)))->gc());
     }
+
+    public function testReadReturnsEmptyArrayForNonStringRedisValues(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->exactly(3))
+            ->method('get')
+            ->willReturnOnConsecutiveCalls(false, null, 123);
+
+        $handler = new RedisSessionHandler($redis);
+
+        $this->assertSame([], $handler->read('a'));
+        $this->assertSame([], $handler->read('b'));
+        $this->assertSame([], $handler->read('c'));
+    }
+
+    #[DataProvider('nonArrayJsonProvider')]
+    public function testReadReturnsEmptyArrayForScalarJson(string $payload): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->method('get')->willReturn($payload);
+
+        $this->assertSame([], (new RedisSessionHandler($redis))->read('scalar'));
+    }
+
+    public static function nonArrayJsonProvider(): array
+    {
+        return [
+            'null' => ['null'],
+            'integer' => ['123'],
+            'string' => ['"value"'],
+            'boolean' => ['true'],
+        ];
+    }
+
+    public function testReadUsesCustomPrefix(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->once())
+            ->method('get')
+            ->with('custom:abc')
+            ->willReturn(json_encode(['ok' => true]));
+
+        $this->assertSame(['ok' => true], (new RedisSessionHandler($redis, 60, 'custom:'))->read('abc'));
+    }
+
+    public function testWriteEncodesUnicodeWithoutEscaping(): void
+    {
+        $data = ['name' => '简'];
+        $json = json_encode($data, JSON_UNESCAPED_UNICODE);
+
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->once())
+            ->method('setex')
+            ->with('fastd:session:abc', 60, $json)
+            ->willReturn(true);
+
+        $this->assertTrue((new RedisSessionHandler($redis, 60))->write('abc', $data));
+    }
+
+    public function testWriteAllowsPayloadAtExactMaxDataSize(): void
+    {
+        $data = ['blob' => str_repeat('x', 32)];
+        $json = json_encode($data, JSON_UNESCAPED_UNICODE);
+
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->once())
+            ->method('setex')
+            ->with('fastd:session:abc', 60, $json)
+            ->willReturn(true);
+
+        $handler = new RedisSessionHandler($redis, 60, 'fastd:session:', strlen($json));
+
+        $this->assertTrue($handler->write('abc', $data));
+    }
+
+    public function testWriteReturnsFalseWhenJsonEncodingFails(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->never())->method('setex');
+
+        $handler = new RedisSessionHandler($redis, 60);
+
+        $this->assertFalse($handler->write('abc', ['invalid' => "\xB1\x31"]));
+    }
+
+    public function testWriteReturnsFalseWhenSetexFails(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->once())
+            ->method('setex')
+            ->willReturn(false);
+
+        $this->assertFalse((new RedisSessionHandler($redis, 60))->write('abc', ['ok' => true]));
+    }
+
+    public function testDestroyReturnsFalseWhenKeyDoesNotExist(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->once())->method('del')->with('fastd:session:missing')->willReturn(0);
+
+        $this->assertFalse((new RedisSessionHandler($redis))->destroy('missing'));
+    }
+
+    public function testExistsReturnsFalseWhenKeyDoesNotExist(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->once())->method('exists')->with('fastd:session:missing')->willReturn(0);
+
+        $this->assertFalse((new RedisSessionHandler($redis))->exists('missing'));
+    }
+
+    public function testGcAcceptsMaxLifetimeAndRemainsNoop(): void
+    {
+        $redis = $this->createMock(Redis::class);
+        $redis->expects($this->never())->method('get');
+        $redis->expects($this->never())->method('setex');
+        $redis->expects($this->never())->method('del');
+
+        $this->assertSame(0, (new RedisSessionHandler($redis))->gc(3600));
+    }
 }