Posts Tagged ‘C#’

As a continuation to my recent rant about the differences between programmers and developers and how programmers love to code and … well, everything it is mentioned in that post, I felt like sharing a little bit of fun I had with this stackoverflow question.

Since it had already been answered and actually there was a little debate going on about the pros and cons of the accepted answer I was about to close it and look for something else when I decided to have a little bit of fun and make the solution generic.

Not like it was difficult, after a couple of minutes I had this:

    public class PropertyValidator
    {
        public bool Validate<T, TResult>(IEnumerable<T> list, Func<T, TResult> expression)
        {
            return list.Select(expression).Distinct().Count() <= 1;
        }
    }

But the fun didn’t end there, since this was not needed in what I was working on I had to demonstrate that it worked by other means, what could those means possibly be? You guessed it, unit tests!

    [TestClass]
    public class SameValueInPropertyValidatorTests
    {
        private PropertyValidator _validator;

        [TestInitialize]
        public void Initialize()
        {
            _validator = new PropertyValidator();
        }

        [TestMethod]
        public void ReturnsTrueIfListIsEmpty()
        {
            var list = new List<string>();
            Func<string, string> expression = x => x;

            var result = _validator.Validate(list, expression);

            Assert.IsTrue(result);
        }

        [TestMethod]
        public void ReturnsTrueWhenValuesAreSameForStrings()
        {
            var list = new List<string> {"1", "1", "1", "1", "1", "1"};
            Func<string, string> expression = x => x;

            var result = _validator.Validate(list, expression);

            Assert.IsTrue(result);
        }

        [TestMethod]
        public void ReturnsFalseWhenValuesAreNotSameForStrings()
        {
            var list = new List<string> { "1", "1", "2", "1", "1", "1" };
            Func<string, string> expression = x => x;

            var result = _validator.Validate(list, expression);

            Assert.IsFalse(result);
        }

        [TestMethod]
        public void ReturnsTrueWhenValuesAreSameForKeyValuePair()
        {
            var list = new List<KeyValuePair<string, int>>
            {
                new KeyValuePair<string, int>("any1", 1),
                new KeyValuePair<string, int>("any2", 1),
                new KeyValuePair<string, int>("any3", 1),
                new KeyValuePair<string, int>("any4", 1),
            };

            Func<KeyValuePair<string, int>, int> expression = x => x.Value;

            var result = _validator.Validate(list, expression);

            Assert.IsTrue(result);
        }

        [TestMethod]
        public void ReturnsFalseWhenValuesAreNotSameForKeyValuePair()
        {
            var list = new List<KeyValuePair<string, int>>
            {
                new KeyValuePair<string, int>("any1", 1),
                new KeyValuePair<string, int>("any2", 1),
                new KeyValuePair<string, int>("any3", 456),
                new KeyValuePair<string, int>("any4", 1),
            };

            Func<KeyValuePair<string, int>, int> expression = x => x.Value;

            var result = _validator.Validate(list, expression);

            Assert.IsFalse(result);
        }

        [TestMethod]
        public void ReturnsTrueWhenValuesAreSameForEnumProperty()
        {
            var list = new List<Car>
            {
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
            };

            Func<Car, Colors> expression = x => x.Color;

            var result = _validator.Validate(list, expression);

            Assert.IsTrue(result);
        }

        [TestMethod]
        public void ReturnsFalseWhenValuesAreNotSameForEnumProperty()
        {
            var list = new List<Car>
            {
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Black},
                new Car {Color = Colors.Red},
            };

            Func<Car, Colors> expression = x => x.Color;

            var result = _validator.Validate(list, expression);

            Assert.IsFalse(result);
        }

    }

And since we were on a roll, why not remove the duplication by creating generic methods to assert the results:

    [TestClass]
    public class SameValueInPropertyValidatorTests
    {
        private PropertyValidator _validator;

        [TestInitialize]
        public void Initialize()
        {
            _validator = new PropertyValidator();
        }

        [TestMethod]
        public void ReturnsTrueIfListIsEmpty()
        {
            var list = new List<string>();
            Func<string, string> expression = x => x;

            AssertIsTrue(list, expression);
        }

        [TestMethod]
        public void ReturnsTrueWhenValuesAreSameForStrings()
        {
            var list = new List<string> { "1", "1", "1", "1", "1", "1" };
            Func<string, string> expression = x => x;

            AssertIsTrue(list, expression);
        }

        [TestMethod]
        public void ReturnsFalseWhenValuesAreNotSameForStrings()
        {
            var list = new List<string> { "1", "1", "2", "1", "1", "1" };
            Func<string, string> expression = x => x;

            AssertIsFalse(list, expression);
        }

        [TestMethod]
        public void ReturnsTrueWhenValuesAreSameForKeyValuePair()
        {
            var list = new List<KeyValuePair<string, int>>
            {
                new KeyValuePair<string, int>("any1", 1),
                new KeyValuePair<string, int>("any2", 1),
                new KeyValuePair<string, int>("any3", 1),
                new KeyValuePair<string, int>("any4", 1),
            };

            Func<KeyValuePair<string, int>, int> expression = x => x.Value;

            AssertIsTrue(list, expression);
        }

        [TestMethod]
        public void ReturnsFalseWhenValuesAreNotSameForKeyValuePair()
        {
            var list = new List<KeyValuePair<string, int>>
            {
                new KeyValuePair<string, int>("any1", 1),
                new KeyValuePair<string, int>("any2", 1),
                new KeyValuePair<string, int>("any3", 456),
                new KeyValuePair<string, int>("any4", 1),
            };

            Func<KeyValuePair<string, int>, int> expression = x => x.Value;

            AssertIsFalse(list, expression);
        }

        [TestMethod]
        public void ReturnsTrueWhenValuesAreSameForEnumProperty()
        {
            var list = new List<Car>
            {
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
            };

            Func<Car, Colors> expression = x => x.Color;

            AssertIsTrue(list, expression);
        }

        [TestMethod]
        public void ReturnsFalseWhenValuesAreNotSameForEnumProperty()
        {
            var list = new List<Car>
            {
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Red},
                new Car {Color = Colors.Black},
                new Car {Color = Colors.Red},
            };

            Func<Car, Colors> expression = x => x.Color;

            AssertIsFalse(list, expression);
        }

        private void AssertIsTrue<T, TResult>(IEnumerable<T> list, Func<T, TResult> expression)
        {
            var result = _validator.Validate(list, expression);

            Assert.IsTrue(result);
        }    

        private void AssertIsFalse<T, TResult>(IEnumerable<T> list, Func<T, TResult> expression)
        {
            var result = _validator.Validate(list, expression);

            Assert.IsFalse(result);
        }    
    }

Not exactly a break through discovery or even a coding kata but still it was a cute exercise for me to kill some time.

Would you like to share your favorite exercises or your sources of inspiration for coding research? I’d love to hear about them.

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Just this week I blogged about how to assert the message of an expected exception and one of the things I was mentioning is how quite some people had proposed different implementations.

Today I found this post from a fellow blogger in which he talks about the MSTest Extensions library. Basically it explains how to install the NuGet package and shows a small example of how to use the ExceptionAssert method to fulfill the need of asserting the thrown exception’s message.

Unfortunately this implementation still suffers from the limitations that we discussed the last time, it can only deal with Actions so if you want to test a method with a return value or a constructor, this option will not provide a solution.

Not everything about this option is bad though, the use of generics is a nice touch so I thought I could include a couple of improvements to the solution I proposed:

    public static class AssertException
    {
        public static void Is<T>(string message, Delegate action, params object[] parameters) where T : Exception
        {
            try
            {
                action.DynamicInvoke(parameters);
                Assert.Fail(string.Format("Expected exception of type <{0}> with message <{1}> but none was thrown.", typeof(T).Name, message));
            }
            catch (Exception ex)
            {
                if (ex is AssertFailedException || ex is AssertInconclusiveException) throw;

                if (ex.InnerException == null)
                {
                    Assert.IsTrue(ex is T, string.Format("Expected exception type: <{0}> Actual: {1}", typeof(T).Name, ex.GetType().Name));
                    Assert.AreEqual(message, ex.Message, true, CultureInfo.InvariantCulture);
                }
                else
                {
                    Assert.IsTrue(ex.InnerException is T, string.Format("Expected exception type: <{0}> Actual: {1}", typeof(T).Name, ex.InnerException.GetType().Name));
                    Assert.AreEqual(message, ex.InnerException.Message, true, CultureInfo.InvariantCulture);
                }
            }
        }

        public static void Is(Exception expected, Delegate action, params object[] parameters)
        {
            try
            {
                action.DynamicInvoke(parameters);
                Assert.Fail(string.Format("Expected exception of type <{0}> with message <{1}> but none was thrown.", expected.GetType().FullName, expected.Message));
            }
            catch (Exception ex)
            {
                if (ex is AssertFailedException || ex is AssertInconclusiveException) throw;

                if (ex.InnerException == null)
                {
                    Assert.IsTrue(expected.GetType().IsInstanceOfType(ex), string.Format("Expected exception type: <{0}> Actual: {1}", expected.GetType().Name, ex.GetType().Name));
                    Assert.AreEqual(expected.Message, ex.Message, true, CultureInfo.InvariantCulture);
                }
                else
                {
                    Assert.IsTrue(expected.GetType().IsInstanceOfType(ex.InnerException), string.Format("Expected exception type: <{0}> Actual: {1}", expected.GetType().Name, ex.InnerException.GetType().Name));
                    Assert.AreEqual(expected.Message, ex.InnerException.Message, true, CultureInfo.InvariantCulture);
                }
            }
        }
    }

As you can see now the class has two overloaded methods, a generic and a non-generic versions. Also the names of both the class and the method changed so it reads a little bit better and finally both now support inherited exceptions.

This is what the use of this class will now look like:

        [TestMethod]
        public void ConstructorThrowsExceptionWhenArgumentsAreInvalid()
        {
           AssertException.Is<ArgumentNullException>("Value cannot be null.\r\nParameter name: number",
              new Func<int?, string, Foo>((num, name) => new Foo(num, name)),
              null, "any");

           AssertException.Is<ArgumentNullException>("Value cannot be null.\r\nParameter name: name",
              new Func<int?, string, Foo>((num, name) => new Foo(num, name)),
              1, string.Empty);

           AssertException.Is(new ArgumentNullException("name"),
              new Func<int?, string, Foo>((num, name) => new Foo(num, name)),
              1, string.Empty);
        }

        [TestMethod]
        public void MethodsThrowExceptions()
        {
            var firstFoo = new Foo(-5, "something");
            AssertException.Is<ApplicationException>("Number should not be negative",
               new Action(firstFoo.DoSomething));

            var secondFoo = new Foo(5, "something");
            AssertException.Is<DivideByZeroException>("Number cannot be divided by zero",
               new Action<int>(secondFoo.DoSomethingElse),
               0);
        }

        [TestMethod]
        public void FunctionsThrowExceptions()
        {
            var foo = new Foo(1, "invalid");

            AssertException.Is<InvalidCredentialException>("Authorization denied",
               new Func<bool>(foo.Validate));

            AssertException.Is<NullReferenceException>("Seriously Foo cannot be null",
               new Func<string, int?, Foo, Foo>(foo.GetNewFoo),
               "any", 3, null);
        }

As you can see the code now almost reads as regular English. It is still more verbose than the attribute option but we discussed the advantages and disadvantages of both approaches on the previous post.

So a couple of conclusions that I can get are that even though we may have a good solution for a particular problem we can always find inspiration and ideas to improve those solutions and we should always be humble enough to realize that our solutions could be improved, no matter how much we might like them.

The same as last time here you have several options to assert the message of exceptions in your unit tests. Use the one you consider the most appropriate. Happy coding.

If you do a quick google search you will realize a lot of people out there have the need to be able to unit test that a piece of code throws an exception with a specific message. Unfortunately the ExpectedExceptionAttribute attribute does not provide this feature. It does have a “message” parameter but its use is to define the message the developer will see when the test fails.

All the people with this need, myself included, have searched long and hard for a way to implement an attribute with this functionality or, at the very least, a way to execute this kind of test reliably and in a way that it can be reused consistently for each possible case.

Most implementations I have found are different flavors of catching the exception and comparing the type and message to an expected one, but they are limited in the number or type of parameters, or on the return type they support. I did once find the implementation of an attribute but was a little disappointed since I thought it was too much code for something as simple as the objective at hand. Let me be very clear about the fact that I am NOT saying this is a bad option nor am I discouraging its use in any way or form. I am only saying that, in my very personal opinion, it is too much code for something so simple and, it is code that you should understand how it works since you might have the need to maintain it.

So because of this I came up with another implementation by using delegates which is smaller than the attribute one and supports both actions and functions with as many parameters as needed. It does have the disadvantage though that its use might be a little cryptic. I always strive for code readability so decorating the test method with an attribute may be a little better. Here is the code, some examples on its use and, for completeness, a Foo class to test it:

This is the code that we are interested in:


public static class CustomAssert
{
   public static void IfExceptionIs(Exception expected, Delegate action, params object[] parameters)
   {
      try
      {
         action.DynamicInvoke(parameters);
         Assert.Fail(string.Format("Expected exception of type <{0}>; with message <{1}> but none was thrown.", expected.GetType().FullName, expected.Message));
      }
      catch (Exception ex)
      {
         if (ex is AssertFailedException || ex is AssertInconclusiveException) throw;

         if (ex.InnerException == null)
         {
             Assert.AreEqual(expected.Message, ex.Message, true, CultureInfo.InvariantCulture);
             Assert.AreEqual(expected.GetType(), ex.GetType());
         }
         else
         {
             Assert.AreEqual(expected.Message, ex.InnerException.Message, true,  CultureInfo.InvariantCulture);
             Assert.AreEqual(expected.GetType(), ex.InnerException.GetType());
         }
      }
   }
}

This would be the testing Foo class:

public class Foo
{
   private readonly int? _number;
   private readonly string _name;

   public Foo(int? number, string name)
   {
      if(!number.HasValue) throw new ArgumentNullException("number");
      if(string.IsNullOrEmpty(name)) throw new ArgumentNullException("name");

      _number = number;
      _name = name;
   }

   public void DoSomething()
   {
      if(_number < 0) throw new ApplicationException("Number should not be negative");
   }

   public void DoSomethingElse(int dividend)
   {
      if(dividend == 0) throw new DivideByZeroException("Number cannot be divided by zero");
   }

   public bool Validate()
   {
      if(_name == "invalid") throw new InvalidCredentialException("Authorization denied");
      return true;
   }

   public Foo GetNewFoo(string newName, int? newNumber, Foo oldFoo)
   {
      if(oldFoo == null) throw new NullReferenceException("Seriously Foo cannot be null");
      return new Foo(newNumber, newName);
   }
}

And this is how it would be used:

[TestMethod]
public void ConstructorThrowsExceptionWhenArgumentsAreInvalid()
{
   CustomAssert.IfExceptionIs(new ArgumentNullException("number"),
      new Func<int?, string, Foo>((num, name) =>; new Foo(num, name)),
      null, "any");

   CustomAssert.IfExceptionIs(new ArgumentNullException("name"),
      new Func<int?, string, Foo>((num, name) => new Foo(num, name)),
      1, string.Empty);
}

[TestMethod]
public void MethodsThrowExceptions()
{
   var firstFoo = new Foo(-5, "something");
   CustomAssert.IfExceptionIs(new ApplicationException("Number should not be negative"),
      new Action(firstFoo.DoSomething));

   var secondFoo = new Foo(5, "something");
   CustomAssert.IfExceptionIs(new DivideByZeroException("Number cannot be divided by zero"),
      new Action<int>(secondFoo.DoSomethingElse),
      0);
}

[TestMethod]
public void FunctionsThrowExceptions()
{
   var foo = new Foo(1, "invalid");

   CustomAssert.IfExceptionIs(new InvalidCredentialException("Authorization denied"),
      new Func<bool>(foo.Validate));

   CustomAssert.IfExceptionIs(new NullReferenceException("Seriously Foo cannot be null"),
      new Func<string, int?, Foo, Foo>(foo.GetNewFoo),
      "any", 3, null);
}

To have the complete picture here are some snippets on how would the tests look like if we were to use the custom attribute:


[TestMethod]
[ExpectedExceptionWithMessage(typeof(ArgumentNullException), "name")]
public void ConstructorThrowsExceptionWhenNameIsEmpty()
{
   new Foo(1, string.Empty);
}

[TestMethod]
[ExpectedExceptionWithMessage(typeof(ApplicationException), "Number should not be negative")]
public void MethodThrowsExceptionWhenNumberIsNegative()
{
   var foo = new Foo(-5, "something");
   foo.DoSomething();
}

Another thing to note is that the implementation I am proposing looks for an inner exception since sometimes the real problem might be hiding in there and the attribute one supports inherited exceptions. Both options could easily be added in either one.

So there you have it, two options to assert the message of an expected exception. Use the one you consider best for you, your team and your project and may your unit tests save you from grief and maintenance nightmares.

In the last few years a lot has been written about the benefits of automated testing, unit testing, TDD, and mocking frameworks. So much has been written about it, even demonstrated in the field, that I find quite surprising, and frightening, that there are some blogs out there in which their authors claim that the effort required to write the tests and let the tests drive the design is a huge overhead, not necessary, increases the complexity of both the production code and the tests themselves, a bad approach among other things.

Unfortunately I was unable to find the exact quote, but I believe that it was in his book, Architecting Applications for the Enterprise, that Dino Esposito says, I am paraphrasing, that there is no difference between a working piece of software that is testable and another one that is not, but the one that is designed with testability in mind will have a much better design. Even though I do not agree with the first part of this claim, the reasons and arguments are the subject of another post, I absolutely agree with the second part of it. When we design our software with testability in mind the end result is a much more maintainable and loosely coupled design.

With these ideas in mind, the next series of posts will aim to address some of the, what I consider, misconceptions about designing for testability, loosely coupling, and the YAGNI and KISS principles. I hope that by the end of them I will be able to add a small contribution to the development community in trying to make software development a more robust discipline.

Designing for testability does pose a number of challenges that have been addressed in a number of ways. One of these ways has been the Inversion of Control (IoC) principle, and more specifically by using Dependency Injection. Another way has been by the creation of tools like TypeMock and Microsoft Fakes. In a nutshell these tools are able to reach into unreachable code and replace static methods and tightly coupled classes with stubs so that untestable code can be unit tested. We will discuss this type of tools at another time, what I am more interested right now is to talk about an online argument in the comments section of this blog post between two people about the use of these tools.

The person who was against the use of this tools was concerned about the unmaintainable and tightly coupled software that could be developed since the limitations of replacing those hard coded dependencies were no longer there. The other person, who was not only in favor of these tools but avidly encouraged their use, claimed that his concerns were the result of the idea of “the ability for code to be unit testable in classical terms” and that the use of an abstract factory would reduce the coupling even further. This last comment was what drew the line for me. Don’t get me wrong, I love the abstract factory pattern and I think is an invaluable tool to abstract the creation of objects from the components that will use them. This does not mean that an abstract factory in itself will be loosely coupled to the code that needs to decide which concrete factory to instantiate and have it create the required object.

To be able to demonstrate these ideas, let’s think about a smart phone manufacturer that has different lines of products and these products can be subdivide into sub-products to satisfy the increasing demands of a hungry market. Of course when the manufactured products reach a certain point in the assembly line a certain number of, what do you know, tests will have to be performed to make sure each product comply with the company’s quality policies. In order to do that all products need to have a common interface to be handed to the testing process, which will not be interested in the exact model of the product.

    public interface IPhone
    {
        void DoSomething();
    }

    public class HighEnd16Gig : IPhone
    {
        public void DoSomething(){}
    }

    public class HighEnd32Gig : IPhone
    {
        public void DoSomething(){}
    }

    public class LowEnd16Gig : IPhone
    {
        public void DoSomething(){}
    }

    public class LowEnd32Gig : IPhone
    {
        public void DoSomething(){}
    }

We can see that we have a high end and a low end phone and that each of them comes in 16 and 32 gigs of storage models. Since the testing process should not care about what kind of phone it will receive at any given time, we define an abstract factory to create the concrete product before starting the tests.

    public interface IPhoneFactory
    {
        IPhone Create();
    }

    public class HighEndFactory : IPhoneFactory
    {
        private readonly StorageSize _storageSize;

        public HighEndFactory(StorageSize storageSize)
        {
            _storageSize = storageSize;
        }

        public IPhone Create()
        {
            switch (_storageSize)
            {
                case StorageSize.Gig16:
                    return new HighEnd16Gig();
                case StorageSize.Gig32:
                    return new HighEnd32Gig();
                default:
                    throw new ArgumentException("Unknown high end model.");
            }
        }
    }

    public class LowEndFactory : IPhoneFactory
    {
        private readonly StorageSize _storageSize;

        public LowEndFactory(StorageSize storageSize)
        {
            _storageSize = storageSize;
        }

        public IPhone Create()
        {
            switch (_storageSize)
            {
                case StorageSize.Gig16:
                    return new LowEnd16Gig();
                case StorageSize.Gig32:
                    return new LowEnd32Gig();
                default:
                    throw new ArgumentException("Unknown low end model.");
            }
        }
    }
    public interface IManufacturingProcess
    {
        void ProcessProduct(ProductType productType, StorageSize storageSize);
    }

    public class TestingCell : IManufacturingProcess
    {
        public void ProcessProduct(ProductType productType, StorageSize storageSize)
        {
            //Do some stuff.

            IPhoneFactory factory;
            switch (productType)
            {
                case ProductType.HighEnd:
                    factory = new HighEndFactory(storageSize);
                    break;
                case ProductType.LowEnd:
                    factory = new LowEndFactory(storageSize);
                    break;
                default:
                    throw new ArgumentException("Unknown Product Type");
            }

            var product = factory.Create();
            ExecuteTests(product);
        }

        private void ExecuteTests(IPhone product)
        {
            product.DoSomething();
        }
    }

This is a very good design, we can see that the component that is going to start the testing process is completely abstracted from the creation mechanism of the different types of products, but there is still one problem, this component is tightly coupled not only to the abstraction but to the two concrete implementations as well. This component is deciding which kind of factory it needs to instantiate to ask for the product it will send to the testing process so if new product lines are added, it will have to be modified to include the new concrete factories and this is a big maintenance issue. Even worse, this is just one step of the whole process, other processes will have to implement the same logic to determine which factory to use.

A much better approach would be to inject the factory to this component so it is completely agnostic of the kind of factory it will be calling.

    public interface IManufacturingProcess
    {
        void ProcessProduct();
    }

    public class TestingCell : IManufacturingProcess
    {
        private readonly IPhoneFactory _factory;

        public TestingCell(IPhoneFactory factory)
        {
            if(factory == null) throw new ArgumentNullException("factory");
            _factory = factory;
        }

        public void ProcessProduct()
        {
            //Do some stuff.

            var product = _factory.Create();
            ExecuteTests(product);
        }

        private void ExecuteTests(IPhone product)
        {
            product.DoSomething();
        }
    }

The benefits of this approach are so many that it just cannot be underestimated:

  • These factories are used by a lot of components throughout the manufacturing process so the code to decide which factory to instantiate will not have to be duplicated in each one.
  • If the factories, the products, and their interfaces are each defined in their own assembly the components that use them only need a reference to the one with the interfaces so, even if new factories are constantly added the assemblies that use them will not have to be recompiled making all of your assemblies truly decoupled.
  • The instantiation of the factories can be isolated in a single place of the application, preferably in the Composition Root.
  • The components that require the factories’ adhere more to the Single Responsibility Principle.
  • The component that will perform the tests can be unit tested in complete isolation without any concern of how the factories create the products.
  • Once you have made your peace with the concepts of abstract factory, dependency injection, and composition root, a nice implementation of all of these concepts working together can be used.

Even though abstract factories are a wonderful tool to isolate and abstract the creation of components from their callers, they are not, in their own sense, a way to achieve a loosely coupled design. To this day the best design technique that I have seen to achieve absolute and truly loose coupling, not only from individual classes but from full assemblies, is dependency injection. I will not presume to say that this is the golden hammer of software engineering, but so far it has proven itself to be the best we’ve got.