Best practices for writing first class unit tests

Writing First Class Unit Tests

Best Practices

Dennis Doomen | Principal Consultant | Aviva Solutions@ddoomen | www.dennisdoomen.net

Unit tests…Are fast

Are automatedAre small

Run in-memory

Unit = Single class…or…

Dennis Doomen

Integration tests…Can cross boundaries

Are slowerCan depend on external

resources

Dennis Doomen

Other forms of testingSystem Testing

Usability TestingUser Acceptance Testing

Dennis Doomen

My First Attempt…

Dennis Doomen

[TestMethod] public void FindCustomersTest1() { var viewModel = new CustomerManagementViewModel(); string propertyChanged = ""; viewModel.PropertyChanged += (sender, args) => propertyChanged = args.PropertyName; viewModel.City = "Washington"; viewModel.MinimumAccountBalance = 10000;

viewModel.Find();

var customers = viewModel.Customers; Assert.AreEqual(2, customers.Count()); Assert.IsTrue(customers.Any(c => c.Id == 15)); Assert.IsTrue(customers.Any(c => c.Id == 81)); Assert.AreEqual("Customers", propertyChanged);

viewModel.City = ""; viewModel.MinimumAccountBalance = 0;

propertyChanged = "";

viewModel.Find();

Assert.AreEqual(102, viewModel.Customers.Count()); }

Intention RevealingSmall and focused

Clear cause and effectTest one condition

IndependentRepeatable

No side-effects

If it is not important for the

test, it is very important not to

show it…

My first attempt…

A small improvement… [TestMethod]

public void When_searching_it_should_account_for_the_city_and_minimal_account_balance() { }

My first attempt…

More improvements…Isolate The Ugly Stuff

Use Dependency Injection

[TestMethod] public void When_searching_it_should_account_for_the_city_and_minimal_account_balance() { var dummyCustomers = new[] { new Customer(), new Customer()};

var service = new ServiceAgentStub(); service.AddDummyCustomers(dummyCustomers);

var viewModel = new CustomerManagementViewModel(service) { City = "Washington", MinimumAccountBalance = 10000 };

string propertyChanged = null; viewModel.PropertyChanged += (sender, args) => propertyChanged = args.PropertyName;

viewModel.Find();

Assert.AreEqual(2, viewModel.Customers.Count()); CollectionAssert.AreEquivalent(viewModel.Customers.ToArray(), dummyCustomers);

Assert.AreEqual("Washington", service.City); Assert.AreEqual(10000, service.MinimumAccountBalance);

Assert.AreEqual("Customers", propertyChanged); }

public class ServiceAgentStub : IServiceAgent { private List<Customer> dummyCustomers = new List<Customer>();

public decimal? MinimumAccountBalance { get; set; } public string City { get; set; }

public void AddDummyCustomers(params Customer[] customers) { dummyCustomers.AddRange(customers); }

public IEnumerable<Customer> FindCustomers(string city, decimal? minimumAccountBalance) { City = city; MinimumAccountBalance = minimumAccountBalance;

return dummyCustomers; } }

Some more intentions…

[TestMethod] public void When_searching_it_should_account_for_the_city_and_minimal_account_balance() { var dummyCustomers = new[] { new Customer(), new Customer()};

var service = new ServiceAgentStub(); service.AddDummyCustomers(customer1, customer2);

[TestMethod] public void When_searching_it_should_account_for_the_city_and_minimal_account_balance() { var someCustomer = new CustomerBuilder().Build(); var someOtherCustomer = new CustomerBuilder().Build();

var theServiceAgent = new ServiceAgentStub(); theServiceAgent.AddDummyCustomers(someCustomer, someOtherCustomer);

public class CustomerBuilder : TestDataBuilder<Customer> { private static long nextId = 1; private string city = "Redmond"; private decimal accountBalance = 100;

protected override Customer OnBuild() { return new Customer { Id = nextId++, City = city, AccountBalance = accountBalance }; }

public CustomerBuilder InCity(string city) { this.city = city; return this; }

public CustomerBuilder WithAccountBalance(decimal accountBalance) { this.accountBalance = accountBalance; return this; } }

Arrange…act…assert…

State versus interaction

Rules to ease unit testing…Test small before you test big

Prefer state-based testingKeep out of the debugger hell

//------------------------------------------------------------------------------------------------------------------- // Assert //------------------------------------------------------------------------------------------------------------------- Assert.AreEqual(2, viewModel.Customers.Count()); var expectedCustomers = new[] { someCustomer, someOtherCustomer}; CollectionAssert.AreEquivalent(viewModel.Customers.ToArray(), expectedCustomers);

Assert.AreEqual("Washington", theServiceAgent.City); Assert.AreEqual(10000, theServiceAgent.MinimumAccountBalance);

Assert.AreEqual("Customers", changedPropertyName);

//------------------------------------------------------------------------------------------------------------------- // Assert //------------------------------------------------------------------------------------------------------------------- viewModel.Customers.Should().Equal(someCustomers);

theServiceAgent.City.Should().Be("Washington"); theServiceAgent.MinimumAccountBalance.Should().Be(10000m);

changedPropertyName.Should().Be("Customers");

AAA versus BDD-style

And now for some faking…

Karl Seguin wrote:Refusing

Getting too excitedTesting everything!Integration testingDiscover mocking

Mocking everythingBecoming effective

28 May 2009Dennis Doomen

Background InformationJeremy’s Laws of TDD, Test Data Builder, Applying Domain Driven Design (Jimmy Nillson), xUnit Patterns

Example Code, FrameworksSilverlight Cookbook, Fake It Easy, Fluent Assertions

Emaildennis.doomen@avivasolutions.nl

Twitter@ddoomen

Blogwww.dennisdoomen.net

Best practices for writing first class unit tests

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