SpecFlow : StepArgumentTransformation

When writting BDD test features and feature steps, we often need to convert strings to types. Testing strings with a serie of if statement within steps does not maximise reusability and readability. The best would be to get the string recognise as a Type every time we use it in a feature without taking care of the conversion.

SpecFlow provides a StepArgumentTransformation attribute to achieve this :

https://github.com/techtalk/SpecFlow/wiki/Step-Argument-Conversions

Exemple :

 [Then(@"the value of the Shoulder mode is (.*) in the method file")]
 public void ThenTheValueOfTheShoulderModeIsDropInTheMethodFile(string shoulderModeString)
 {
     ShoulderModeType shoulderMode = ShoulderModeType.OFF; ;
     if (ShoulderModeType.Drop.ToString() == shoulderModeString) shoulderMode = ShoulderModeType.Drop;
     else if (ShoulderModeType.OFF.ToString() == shoulderModeString) shoulderMode = ShoulderModeType.OFF;
     else if (ShoulderModeType.Tangential.ToString() == shoulderModeString) shoulderMode = ShoulderModeType.Tangential;
     else Assert.Fail("Invalid shoulderModeString: " + shoulderModeString);
...
     Assert.AreEqual(expectedShouldMode, shoulderMode)
}

Can be refactored as 

[StepArgumentTransformation]
public ShoulderModeType ShoulderModeTransform(string shoulderModeString)
{
     ShoulderModeType shoulderMode = ShoulderModeType.OFF;
     if (ShoulderModeType.Drop.ToString() == shoulderModeString) shoulderMode = ShoulderModeType.Drop;
     else if (ShoulderModeType.OFF.ToString() == shoulderModeString) shoulderMode = ShoulderModeType.OFF;
     else if (ShoulderModeType.Tangential.ToString() == shoulderModeString) shoulderMode = ShoulderModeType.Tangential;
     else Debug.Assert.Fail("Invalid shoulderModeString: " + shoulderModeString);
     return shoulderMode;
}

[Then(@"the value of the Shoulder mode is (.*) in the method file")]
public void ThenTheValueOfTheShoulderModeIsDropInTheMethodFile(ShoulderModeType shoulderMode)
{
   ...  
   Assert.AreEqual(expectedShouldMode, shoulderMode)
}