diff --git a/src/Exception/InvalidStatusException.php b/src/Exception/InvalidStatusException.php
deleted file mode 100644
index 42d0cf31..00000000
--- a/src/Exception/InvalidStatusException.php
+++ /dev/null
@@ -1,48 +0,0 @@
-<?php
-
-declare(strict_types=1);
-
-namespace Yiisoft\Queue\Exception;
-
-use InvalidArgumentException;
-use Throwable;
-use Yiisoft\FriendlyException\FriendlyExceptionInterface;
-
-class InvalidStatusException extends InvalidArgumentException implements FriendlyExceptionInterface
-{
-    private int $status;
-
-    public function __construct(int $status, string $message = '', int $code = 0, Throwable $previous = null)
-    {
-        if ($message === '') {
-            $message = "Invalid status provided: $status";
-        }
-        parent::__construct($message, $code, $previous);
-        $this->status = $status;
-    }
-
-    public function getName(): string
-    {
-        return 'Invalid job status provided';
-    }
-
-    public function getSolution(): ?string
-    {
-        return <<<SOLUTION
-            Default available status values are:
-            [1] JobStatus::WAITING
-            [2] JobStatus::RESERVED
-            [3] JobStatus::DONE
-
-            Please consider using one of them or extending \Yiisoft\Queue\Enum\JobStatus class with your ows values.
-            SOLUTION;
-    }
-
-    /**
-     * Get the wrong status value
-     */
-    public function getStatus(): int
-    {
-        return $this->status;
-    }
-}
diff --git a/src/Message/EnvelopeTrait.php b/src/Message/EnvelopeTrait.php
index e8d19d65..68ae0d88 100644
--- a/src/Message/EnvelopeTrait.php
+++ b/src/Message/EnvelopeTrait.php
@@ -15,7 +15,7 @@ abstract public static function fromMessage(MessageInterface $message): self;
 
     public static function fromData(string $handlerName, mixed $data, array $metadata = []): MessageInterface
     {
-        return self::fromMessage(Message::fromData($handlerName, $data, $metadata));
+        return static::fromMessage(Message::fromData($handlerName, $data, $metadata));
     }
 
     public function getMessage(): MessageInterface
@@ -46,8 +46,8 @@ public function getMetadata(): array
         return array_merge(
             $this->message->getMetadata(),
             [
-                self::ENVELOPE_STACK_KEY => array_merge(
-                    $this->message->getMetadata()[self::ENVELOPE_STACK_KEY] ?? [],
+                EnvelopeInterface::ENVELOPE_STACK_KEY => array_merge(
+                    $this->message->getMetadata()[EnvelopeInterface::ENVELOPE_STACK_KEY] ?? [],
                     [self::class],
                 ),
             ],
diff --git a/tests/App/DummyEnvelope.php b/tests/App/DummyEnvelope.php
new file mode 100644
index 00000000..65c6162f
--- /dev/null
+++ b/tests/App/DummyEnvelope.php
@@ -0,0 +1,22 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Queue\Tests\App;
+
+use Yiisoft\Queue\Message\EnvelopeInterface;
+use Yiisoft\Queue\Message\EnvelopeTrait;
+use Yiisoft\Queue\Message\MessageInterface;
+
+final class DummyEnvelope implements EnvelopeInterface
+{
+    use EnvelopeTrait;
+
+    public static function fromMessage(MessageInterface $message): self
+    {
+        $instance = new self();
+        $instance->message = $message;
+
+        return $instance;
+    }
+}
diff --git a/tests/App/StaticMessageHandler.php b/tests/App/StaticMessageHandler.php
new file mode 100644
index 00000000..3825836a
--- /dev/null
+++ b/tests/App/StaticMessageHandler.php
@@ -0,0 +1,15 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Queue\Tests\App;
+
+class StaticMessageHandler
+{
+    public static bool $wasHandled = false;
+
+    public static function handle(): void
+    {
+        self::$wasHandled = true;
+    }
+}
diff --git a/tests/Unit/Command/SoftLimitTraitTest.php b/tests/Unit/Command/SoftLimitTraitTest.php
new file mode 100644
index 00000000..fe034a5a
--- /dev/null
+++ b/tests/Unit/Command/SoftLimitTraitTest.php
@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Queue\Tests\Unit\Command;
+
+use PHPUnit\Framework\TestCase;
+use Yiisoft\Queue\Cli\SoftLimitTrait;
+
+final class SoftLimitTraitTest extends TestCase
+{
+    public function testMemoryLimitNotReachedWhenLimitIsZero(): void
+    {
+        $instance = new class () {
+            use SoftLimitTrait {
+                memoryLimitReached as public;
+            }
+
+            protected function getMemoryLimit(): int
+            {
+                return 0;
+            }
+        };
+
+        $this->assertFalse($instance->memoryLimitReached());
+    }
+
+    public function testMemoryLimitNotReachedWhenUsageIsLower(): void
+    {
+        $currentMemoryUsage = memory_get_usage(true);
+        $instance = new class ($currentMemoryUsage + 1024 * 1024) { // 1MB higher than current usage
+            use SoftLimitTrait {
+                memoryLimitReached as public;
+            }
+
+            public function __construct(private int $limit)
+            {
+            }
+
+            protected function getMemoryLimit(): int
+            {
+                return $this->limit;
+            }
+        };
+
+        $this->assertFalse($instance->memoryLimitReached());
+    }
+
+    public function testMemoryLimitReachedWhenUsageIsHigher(): void
+    {
+        $currentMemoryUsage = memory_get_usage(true);
+        $instance = new class ($currentMemoryUsage - 1024) { // 1KB lower than current usage
+            use SoftLimitTrait {
+                memoryLimitReached as public;
+            }
+
+            public function __construct(private int $limit)
+            {
+            }
+
+            protected function getMemoryLimit(): int
+            {
+                return $this->limit;
+            }
+        };
+
+        $this->assertTrue($instance->memoryLimitReached());
+    }
+
+    public function testMemoryLimitExceededWhenUsageIncreases(): void
+    {
+        $currentMemoryUsage = memory_get_usage(true);
+        $instance = new class ($currentMemoryUsage + 5 * 1024 * 1024) { // Set limit 5MB higher than current usage
+            use SoftLimitTrait {
+                memoryLimitReached as public;
+            }
+
+            public function __construct(private int $limit)
+            {
+            }
+
+            protected function getMemoryLimit(): int
+            {
+                return $this->limit;
+            }
+        };
+
+        // Initially memory limit is not reached
+        $this->assertFalse($instance->memoryLimitReached());
+
+        // Create a large string to increase memory usage
+        $largeString = str_repeat('x', 5 * 1024 * 1024 + 1); // 5MB and 1 byte string
+
+        // Now memory limit should be exceeded
+        $this->assertTrue($instance->memoryLimitReached());
+
+        // Clean up to free memory
+        unset($largeString);
+    }
+}
diff --git a/tests/Unit/Message/EnvelopeTraitTest.php b/tests/Unit/Message/EnvelopeTraitTest.php
new file mode 100644
index 00000000..5dd5c4a6
--- /dev/null
+++ b/tests/Unit/Message/EnvelopeTraitTest.php
@@ -0,0 +1,49 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Yiisoft\Queue\Tests\Unit\Message;
+
+use PHPUnit\Framework\TestCase;
+use Yiisoft\Queue\Message\Message;
+use Yiisoft\Queue\Tests\App\DummyEnvelope;
+
+final class EnvelopeTraitTest extends TestCase
+{
+    private function createTestEnvelope(): DummyEnvelope
+    {
+        return new DummyEnvelope();
+    }
+
+    public function testFromData(): void
+    {
+        $handlerName = 'test-handler';
+        $data = ['key' => 'value'];
+        $metadata = ['meta' => 'data'];
+
+        $envelope = DummyEnvelope::fromData($handlerName, $data, $metadata);
+
+        $this->assertInstanceOf(DummyEnvelope::class, $envelope);
+        $this->assertSame($handlerName, $envelope->getHandlerName());
+        $this->assertSame($data, $envelope->getData());
+        $this->assertArrayHasKey('meta', $envelope->getMetadata());
+        $this->assertSame('data', $envelope->getMetadata()['meta']);
+    }
+
+    public function testWithMessage(): void
+    {
+        $originalMessage = new Message('original-handler', 'original-data');
+        $newMessage = new Message('new-handler', 'new-data');
+
+        $envelope = $this->createTestEnvelope();
+        $envelope = $envelope->withMessage($originalMessage);
+
+        $this->assertSame($originalMessage, $envelope->getMessage());
+
+        $newEnvelope = $envelope->withMessage($newMessage);
+
+        $this->assertNotSame($envelope, $newEnvelope);
+        $this->assertSame($newMessage, $newEnvelope->getMessage());
+        $this->assertSame($originalMessage, $envelope->getMessage());
+    }
+}
diff --git a/tests/Unit/Message/JsonMessageSerializerTest.php b/tests/Unit/Message/JsonMessageSerializerTest.php
index 18bc5ed9..93889d3b 100644
--- a/tests/Unit/Message/JsonMessageSerializerTest.php
+++ b/tests/Unit/Message/JsonMessageSerializerTest.php
@@ -5,6 +5,7 @@
 namespace Yiisoft\Queue\Tests\Unit\Message;
 
 use InvalidArgumentException;
+use PHPUnit\Framework\Attributes\DataProvider;
 use PHPUnit\Framework\TestCase;
 use Yiisoft\Queue\Message\EnvelopeInterface;
 use Yiisoft\Queue\Message\IdEnvelope;
@@ -18,6 +19,55 @@
  */
 final class JsonMessageSerializerTest extends TestCase
 {
+    /**
+     * @dataProvider dataUnsupportedHandlerNameFormat
+     */
+    #[DataProvider('dataUnsupportedHandlerNameFormat')]
+    public function testHandlerNameFormat(mixed $name): void
+    {
+        $payload = ['name' => $name, 'data' => 'test'];
+        $serializer = $this->createSerializer();
+
+        $this->expectExceptionMessage(sprintf('Handler name must be a string. Got %s.', get_debug_type($name)));
+        $this->expectException(InvalidArgumentException::class);
+        $serializer->unserialize(json_encode($payload));
+    }
+
+    public static function dataUnsupportedHandlerNameFormat(): iterable
+    {
+        yield 'number' => [1];
+        yield 'boolean' => [true];
+        yield 'null' => [null];
+        yield 'array' => [[]];
+    }
+
+    public function testDefaultMessageClassFallbackWrongClass(): void
+    {
+        $serializer = $this->createSerializer();
+        $payload = [
+            'name' => 'handler',
+            'data' => 'test',
+            'meta' => [
+                'message-class' => 'NonExistentClass',
+            ],
+        ];
+
+        $message = $serializer->unserialize(json_encode($payload));
+        $this->assertInstanceOf(Message::class, $message);
+    }
+
+    public function testDefaultMessageClassFallbackClassNotSet(): void
+    {
+        $serializer = $this->createSerializer();
+        $payload = [
+            'name' => 'handler',
+            'data' => 'test',
+            'meta' => [],
+        ];
+        $message = $serializer->unserialize(json_encode($payload));
+        $this->assertInstanceOf(Message::class, $message);
+    }
+
     /**
      * @dataProvider dataUnsupportedPayloadFormat
      */
diff --git a/tests/Unit/WorkerTest.php b/tests/Unit/WorkerTest.php
index d0fc9733..74bbf539 100644
--- a/tests/Unit/WorkerTest.php
+++ b/tests/Unit/WorkerTest.php
@@ -18,6 +18,7 @@
 use Yiisoft\Queue\Middleware\FailureHandling\MiddlewareFactoryFailureInterface;
 use Yiisoft\Queue\QueueInterface;
 use Yiisoft\Queue\Tests\App\FakeHandler;
+use Yiisoft\Queue\Tests\App\StaticMessageHandler;
 use Yiisoft\Queue\Tests\TestCase;
 use Yiisoft\Queue\Worker\Worker;
 
@@ -199,4 +200,57 @@ private function createWorkerByParams(
             new FailureMiddlewareDispatcher($this->createMock(MiddlewareFactoryFailureInterface::class), []),
         );
     }
+
+    public function testHandlerNotFoundInContainer(): void
+    {
+        $message = new Message('nonexistent', ['test-data']);
+        $logger = new SimpleLogger();
+        $container = new SimpleContainer();
+        $handlers = [];
+
+        $queue = $this->createMock(QueueInterface::class);
+        $worker = $this->createWorkerByParams($handlers, $logger, $container);
+
+        $this->expectException(\RuntimeException::class);
+        $this->expectExceptionMessage('Queue handler with name "nonexistent" does not exist');
+        $worker->process($message, $queue);
+    }
+
+    public function testHandlerInContainerNotImplementingInterface(): void
+    {
+        $message = new Message('invalid', ['test-data']);
+        $logger = new SimpleLogger();
+        $container = new SimpleContainer([
+            'invalid' => new class () {
+                public function handle(): void
+                {
+                }
+            },
+        ]);
+        $handlers = [];
+
+        $queue = $this->createMock(QueueInterface::class);
+        $worker = $this->createWorkerByParams($handlers, $logger, $container);
+
+        $this->expectException(\RuntimeException::class);
+        $this->expectExceptionMessage('Queue handler with name "invalid" does not exist');
+        $worker->process($message, $queue);
+    }
+
+    public function testStaticMethodHandler(): void
+    {
+        $message = new Message('static-handler', ['test-data']);
+        $logger = new SimpleLogger();
+        $container = new SimpleContainer();
+        $handlers = [
+            'static-handler' => StaticMessageHandler::handle(...),
+        ];
+
+        $queue = $this->createMock(QueueInterface::class);
+        $worker = $this->createWorkerByParams($handlers, $logger, $container);
+
+        StaticMessageHandler::$wasHandled = false;
+        $worker->process($message, $queue);
+        $this->assertTrue(StaticMessageHandler::$wasHandled);
+    }
 }