diff --git a/tests/src/Codec/StringCodecTest.php b/tests/src/Codec/StringCodecTest.php
index 258c1db..08e92bd 100644
--- a/tests/src/Codec/StringCodecTest.php
+++ b/tests/src/Codec/StringCodecTest.php
@@ -2,6 +2,7 @@
 
 namespace Ramsey\Uuid\Test\Codec;
 
+use Ramsey\Uuid\Codec\StringCodec;
 use Ramsey\Uuid\Test\TestCase;
 
 /**
@@ -11,24 +12,68 @@ use Ramsey\Uuid\Test\TestCase;
  */
 class StringCodecTest extends TestCase
 {
+
+    private $builder;
+    private $uuid;
+    private $fields;
+
+    public function setUp()
+    {
+        parent::setUp();
+        $this->builder = $this->getMock('Ramsey\Uuid\Builder\UuidBuilderInterface');
+        $this->uuid = $this->getMock('Ramsey\Uuid\UuidInterface');
+        $this->fields = ['time_low' => '12345678',
+            'time_mid' => '1234',
+            'time_hi_and_version' => 'abcd',
+            'clock_seq_hi_and_reserved' => 'ab',
+            'clock_seq_low' => 'ef',
+            'node' => '1234abcd4321'];
+    }
+
+    public function tearDown()
+    {
+        parent::tearDown();
+        $this->builder = null;
+        $this->fields = null;
+    }
+
     public function testEncodeUsesFieldsArray()
     {
-
+        $this->uuid->expects($this->once())
+            ->method('getFieldsHex')
+            ->willReturn($this->fields);
+        $codec = new StringCodec($this->builder);
+        $codec->encode($this->uuid);
     }
 
     public function testEncodeReturnsFormattedString()
     {
+        $this->uuid->method('getFieldsHex')
+            ->willReturn($this->fields);
+        $expected = '12345678-1234-abcd-abef-1234abcd4321';
 
+        $codec = new StringCodec($this->builder);
+        $result = $codec->encode($this->uuid);
+        $this->assertEquals($expected, $result);
     }
 
     public function testEncodeBinaryUsesHexadecimalValue()
     {
-
+        $this->uuid->expects($this->once())
+            ->method('getHex')
+            ->willReturn('123456781234abcdabef1234abcd4321');
+        $codec = new StringCodec($this->builder);
+        $codec->encodeBinary($this->uuid);
     }
 
     public function testEncodeBinaryReturnsBinaryString()
     {
-
+        $expected = hex2bin('123456781234abcdabef1234abcd4321');
+        $this->uuid->method('getHex')
+            ->willReturn('123456781234abcdabef1234abcd4321');
+        $codec = new StringCodec($this->builder);
+        $result = $codec->encodeBinary($this->uuid);
+        $this->assertEquals($expected, $result);
     }
 
     public function testDecodeUsesBulderOnFields()
@@ -43,7 +88,7 @@ class StringCodecTest extends TestCase
 
     public function testDecodeBytesThrowsExceptionWhenBytesStringNotSixteenCharacters()
     {
-        
+
     }
 
     public function testDecodeBytesReturnsUuid()