best practices for writing first class unit tests

© 2011 Aviva Solutions 12 april 2023

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…

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Integration tests…Can cross boundaries

Are slowerCan depend on external

resources

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Other forms of testingSystem Testing

Usability TestingUser Acceptance Testing

ATDD

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My First Attempt…

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[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…

© 2011 Aviva Solutions 12 april 2023My 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");

http://fluentassertions.codeplex.com/


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

http://codebetter.com/blogs/jeremy.miller/archive/tags/Test%20Driven%20Development/default.aspx




http://nat.truemesh.com/archives/000714.html

http://www.amazon.com/Applying-Domain-Driven-Design-Patterns-Examples/dp/0321268202




http://xunitpatterns.com/



http://www.silverlightcookbook.com/



http://code.google.com/p/fakeiteasy/





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Twitter@ddoomen

Blogwww.dennisdoomen.net

best practices for writing first class unit tests

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