Multiple Binding Attributes in SpecFlow

I recently discovered something rather nice in SpecFlow, I was implementing a scenario like this

Scenario: Save a user
Given I have a user with the name Joe Bloggs
When I save them
Then the user should have a FirstName Joe
And the user should have a LastName of Bloggs

I wanted to provide the flexibility in the assertions so our QA could decide how he wanted to phrase the text in the scenario. Logically however we’d want the same binding for each variation.

Here’s what I came up with:

[Then(@"the user should have a (.*) (.*)")]
[Then(@"the user should have a (.*) of (.*)")]
public void ThenTheUserShouldHaveA(string field, string value)
{
  var user = GetUser();
  Assert.AreEqual(user.Properties[field], value);
}

However this didn’t work, I kept getting a field of “FirstName of”. I discovered however that you can reverse the binding attributes to give priority.

Updating the attributes to

[Then(@"the user should have a (.*) of (.*)")]
[Then(@"the user should have a (.*) (.*)")]

This change gave the of binding precedence and ensured that both scenario steps worked correctly.

Why write Unit Tests?

Testing is a passion of mine and it’s something I expect to write about a lot more in the future. What I feel is discussed less often though is “Why are we writing tests?”

When many people talk about writing tests they talk about writing Unit Tests, classes and methods broken down into small, isolated areas of code which can be examined with tests to guarantee code quality. Let’s look at an example:

public string ReadText(string filename)
{
  if(File.Exists(filename))
  {
    return File.ReadAllText(filename);
  }
  else
  {
    return null;
  }
}

This code reads the text in a file and returns it, if the file doesn’t exist it returns null.

The thing is, this is trivial code. Writing Unit Tests for something like this is overkill surely? That thirty minutes or so could be invested in the next feature, a bug fix or meeting the tight deadline.

Let’s suppose another developer comes along in a few years time, they see this method and know something their predecessor didn’t. .NET has a FileNotFoundException exception! Deciding to be a conscientious coder they update the method to throw an appropriate exception if the file isn’t found.

public string ReadText(string filename)
{
  if(File.Exists(filename))
  {
    return File.ReadAllText(filename);
  }
  else
  {
    throw new FileNotFoundException(string.Format("The file '{0}' was not found", filename));
  }
}

Unfortunately our conscientious developer missed something. One of the myriad of methods which calls our methods is GetOrCreateFileWithContents

public string GetOrCreateFileWithContents(string filename, string defaultContents)
{
  var currentContents = ReadText(filename);
  if(currentContents == null)
  {
    currentContents = CreateFile(filename, defaultContents);
  }

  return currentContents;
}

Because of our change this method now fails, ReadText throws an exception and the new file is never created in it’s place. This may be an oversimplified example with an overzealous and (dare I say it careless) tidy up but it illustrates the risks we take every day when refactoring and improving code.

This is the true value of Unit Tests, not in finding bugs but in defining the behaviour of the method. If our original developer had invested that extra thirty minutes our Boy Scout would have had some warning when then tried to update the method, they’d have seen that they’d changed the behaviour of the class in an unacceptable way and wouldn’t have made their changes.

The moral of the story? Unit Tests may seem like overkill while you’re writing them. But spare a thought for the poor soul who’s trying to read your methods in a few years time… Leave them a map, a series of executable tests which guarantee that your required behaviour remains unchanged. Your thirty minutes could save them hours, prevent bugs being introduced and help keep your application stable.

SpecFlow what is it and why should I care?

I was introduced to SpecFlow a year or so ago by a friend of mine during a presentation at Agile Yorkshire. He described it as a tool for BDD and I was immediately struck by the revolutionary concept of human readable tests. It’s taken me a little time, some projects and many follow up questions but I feel I’m really beginning to grasp the power of this easy to use tool.

So what is it? SpecFlow is a framework which translates text into a series of steps which are compiled as a test.

This makes more sense with an example. Let’s say I’m the developing the software for a cash machine.


Given I have £150 in the bank
When I withdraw £100
Then I should have £50 remaining in my account

SpecFlow will then generate three steps for you to implement.

[Binding]
public class Bindings
{
  [Given(@"I have £(.*) in the bank")]
  public void GivenIHaveInTheBank(int p0)
  {
    ScenarioContext.Current.Pending();
  }

  [When(@"I withdraw £(.*)")]
  public void WhenIWithdraw(int p0)
  {
    ScenarioContext.Current.Pending();
  }

  [Then(@"I should have £(.*) remaining in my account")]

  public void ThenIShouldHaveRemainingInMyAccount(int p0)
  {
    ScenarioContext.Current.Pending();
  }
}

I’ve filled these in quickly to give you an idea of how the process is intended to work.

[Binding]
public class Bindings
{
  private readonly CashMachine _cashMachine;

  public Bindings(CashMachine cashMachine)
  {
    _cashMachine = cashMachine;
  }

  [Given(@"I have £(.*) in the bank")]
  public void GivenIHaveInTheBank(decimal initialBalance)
  {
    _cashMachine.Balance = initialBalance;
  }

  [When(@"I withdraw £(.*)")]
  public void WhenIWithdraw(decimal withdrawlAmount)
  {

    _cashMachine.Withdraw(withdrawlAmount);

  }

  [Then(@"I should have £(.*) remaining in my account")]
  public void ThenIShouldHaveRemainingInMyAccount(decimal expectedRemainingBalance)
  {
    Assert.AreEqual(expectedRemainingBalance, _cashMachine.Balance);
  }
}

Behind the scenes SpecFlow has built a test using your test framework of choice (MSTest, NUnit, XUnit or a variety of others). These tests can be run within Visual Studio as any other unit test. Here’s my scenario running in Resharper:

 

Resharper Executing Test

 

I think most people would be impressed by this. SpecFlow has converted human readable text and enabled us to write a simple unit test for it. We can easily add a second to make sure that our new state of the art cash machine can also dispense pennies.


Given I have £100.86 in the bank
When I withdraw £1.99
Then I should have £98.87 remaining in my account

We can add additional complexity such as overdrafts


Given I have £100 in the bank
And I have an overdraft of £50
When I withdraw £125
Then I should have £-25 remaining in my account

Or functionality to check that I cannot go overdrawn


Given I have £100 in the bank
And I have an overdraft of £0
When I withdraw £125
Then I should be prevented from withdrawing money
And I should have £100 remaining in my account

I’m sure you can see the value of having simple, understandable definitions of what a particular area of code should do instead of the complicated, developer-only Unit Tests which litter many of today’s solutions. If you wish these executable tests can form the basis of your specs, documentation and even training. Your Product Owner can get involved and validate the tests are correct, if they’re particularly tech-savvy they may even write a few themselves!

What I particularly love about SpecFlow however is the way it empowers today’s QAs. From the moment the first bindings have been created your QA team can be let loose to create new tests, verify edge cases and prove alternate scenarios until they are happy that the feature works as designed. Tests can now be created alongside the features being developed, Acceptance Tests can be created directly from the specification which the QA team can use to validate each feature and scenario as it is being developed. These same tests then form the basis of your regression suite for years to come.

Should any of these tests fail the QA team can provide the developer with not only the human readable replication steps but with with an executable test which can be debugged on the dev’s own PC.

I find this very exciting, we’ve started using SpecFlow for a number of projects and I have every intention of using it for more. If you’re interested in finding out more visit the SpecFlow website or read their Quick Start Guide.