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 automated
Are small
Run in-memory
Unit = Single class…or…
Dennis Doomen

Integration tests…
Can cross boundaries
Are slower
Candepend on external resources
Dennis Doomen

Otherforms of testing
System Testing
UsabilityTesting
User AcceptanceTesting
ATDD
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()); }
IntentionRevealing
Small andfocused
Clearcauseand effect
Test onecondition
Independent
Repeatable
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…

My first attempt…
More improvements…
Isolate The Ugly Stuff
UseDependencyInjection

[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; } }

My first attempt…
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; } }

My first attempt…
Arrange…act…assert…

My first attempt…
State versus interaction

My first attempt…
Rules toease unit testing…
Test small beforeyou test big
Prefer state-basedtesting
Keep 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");

My first attempt…
AAA versus BDD-style

Andnowforsomefaking…

Karl Seguin wrote:
Refusing
Getting too excited
Testing everything!
Integration testing
Discover mocking
Mocking everything
Becoming effective
28 May 2009
Dennis Doomen

Background InformationJeremy’sLaws of TDD, Test Data Builder, Applying Domain Driven Design (Jimmy Nillson), xUnitPatterns
Example Code, FrameworksSilverlightCookbook, Fake It Easy, FluentAssertions

Emaildennis.doomen@avivasolutions.nl
Twitter
@ddoomen
Blogwww.dennisdoomen.net

Best practices for writing first class unit tests

by Dennis Doomen on Dec 11, 2010

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