diff --git a/src/Contract/ParserInterface.php b/src/Contract/ParserInterface.php
new file mode 100644
index 0000000..b45ad91
--- /dev/null
+++ b/src/Contract/ParserInterface.php
@@ -0,0 +1,10 @@
+<?php
+
+namespace Ouxsoft\LuckByDice\Contract;
+
+interface ParserInterface
+{
+
+    public function run($expression) : array;
+
+}
\ No newline at end of file
diff --git a/src/Contract/TurnInterface.php b/src/Contract/TurnInterface.php
new file mode 100644
index 0000000..a5ec763
--- /dev/null
+++ b/src/Contract/TurnInterface.php
@@ -0,0 +1,23 @@
+<?php
+
+namespace Ouxsoft\LuckByDice\Contract;
+
+use Ouxsoft\LuckByDice\Cup;
+use Ouxsoft\LuckByDice\Parser;
+
+interface TurnInterface
+{
+
+    public function __construct(
+        Parser $parser,
+        Cup $cup,
+        string $expression = null
+    );
+
+    public function set(string $expression) : void;
+
+    public function roll() : int;
+
+    public function __toString() : string;
+
+}
\ No newline at end of file
diff --git a/src/Parser.php b/src/Parser.php
index ed44976..97e725a 100644
--- a/src/Parser.php
+++ b/src/Parser.php
@@ -10,7 +10,9 @@
 
 namespace Ouxsoft\LuckByDice;
 
-class Parser
+use Ouxsoft\LuckByDice\Contract\ParserInterface;
+
+class Parser implements ParserInterface
 {
     /**
      * @param $expression
diff --git a/src/Turn.php b/src/Turn.php
index a17cc92..7bd03a2 100644
--- a/src/Turn.php
+++ b/src/Turn.php
@@ -12,11 +12,13 @@
 
 namespace Ouxsoft\LuckByDice;
 
+use Ouxsoft\LuckByDice\Contract\TurnInterface;
+
 /**
  * Class Turn
  * @package Ouxsoft\LuckByDice
  */
-class Turn
+class Turn implements TurnInterface
 {
     /**
      * @var Cup
@@ -32,7 +34,7 @@ class Turn
     private $total;
 
     /**
-     * Expression constructor.
+     * Turn constructor.
      * @param Parser $parser
      * @param Cup $cup
      * @param string|null $expression
@@ -52,6 +54,7 @@ public function __construct(
     }
 
     /**
+     * Set dice notation
      * @param string $expression "1d4+3*2,1d5,d5,10d5"
      */
     public function set(string $expression) : void
@@ -83,4 +86,4 @@ public function __toString() : string
     {
         return (string) $this->total;
     }
-}
+}
\ No newline at end of file
diff --git a/tests/src/Unit/TurnTest.php b/tests/src/Unit/TurnTest.php
index 1e050de..f952013 100644
--- a/tests/src/Unit/TurnTest.php
+++ b/tests/src/Unit/TurnTest.php
@@ -27,6 +27,16 @@ public function tearDown(): void
         unset($this->turn);
     }
 
+    /**
+     * @covers \Ouxsoft\LuckByDice\Turn::set
+     */
+    public function testSet()
+    {
+        $this->turn->set("d3+3*3");
+        $outcome = $this->turn->roll();
+        $this->assertIsInt($outcome);
+    }
+
     /**
      * @covers \Ouxsoft\LuckByDice\Turn::roll
      */
@@ -37,4 +47,14 @@ public function testRoll()
         $this->assertIsInt($outcome);
     }
 
+    /**
+     * @covers \Ouxsoft\LuckByDice\Turn::__toString
+     */
+    public function test__toString()
+    {
+        $this->turn->set("d6");
+        $outcome = (string) $this->turn;
+        $this->assertIsString($outcome);
+    }
+
 }