diff --git a/test/unit/Web3ApiTest.php b/test/unit/Web3ApiTest.php
index a46f504..4b365c3 100644
--- a/test/unit/Web3ApiTest.php
+++ b/test/unit/Web3ApiTest.php
@@ -3,6 +3,7 @@
 namespace Test\Unit;
 
 use RuntimeException;
+use InvalidArgumentException;
 use Test\TestCase;
 
 class Web3ApiTest extends TestCase
@@ -113,4 +114,18 @@ class Web3ApiTest extends TestCase
             $this->assertTrue(true);
         });
     }
+
+    /**
+     * testWrongCallback
+     * 
+     * @return void
+     */
+    public function testWrongCallback()
+    {
+        $this->expectException(InvalidArgumentException::class);
+
+        $web3 = $this->web3;
+
+        $web3->sha3('hello world');
+    }
 }
\ No newline at end of file
diff --git a/test/unit/Web3Test.php b/test/unit/Web3Test.php
index aee0a4c..bbd05eb 100644
--- a/test/unit/Web3Test.php
+++ b/test/unit/Web3Test.php
@@ -49,7 +49,8 @@ class Web3Test extends TestCase
      */
     public function testInstance()
     {
-        $web3 = $this->web3;
+        $requestManager = new HttpRequestManager('http://localhost:8545');
+        $web3 = new Web3(new HttpProvider($requestManager));
 
         $this->assertTrue($web3->provider instanceof HttpProvider);
         $this->assertTrue($web3->provider->requestManager instanceof RequestManager);
@@ -72,5 +73,21 @@ class Web3Test extends TestCase
         $web3->provider = new HttpProvider($requestManager);
 
         $this->assertEquals($web3->provider->requestManager->host, 'http://localhost:8545');
+
+        $web3->provider = null;
+        $this->assertEquals($web3->provider->requestManager->host, 'http://localhost:8545');
+    }
+
+    /**
+     * testCallThrowRuntimeException
+     * 
+     * @return void
+     */
+    public function testCallThrowRuntimeException()
+    {
+        $this->expectException(RuntimeException::class);
+
+        $web3 = new Web3(null);
+        $web3->sha3('hello world');
     }
 }
\ No newline at end of file