Writing good unit tests
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Writing good unit tests AgileKZN – November 2012 © Chillisoft 2012 1
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A brief presentation on some aspects of good unit tests and anti-patterns to watch out to avoid when writing unit tests.
Transcript of Writing good unit tests
Writing good unit testsAgileKZN – November 2012© Chillisoft 2012
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“legacy code is simply code without tests” - Michael Feathers
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What is a Unit Test?
My System
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Unit tests are:
1. Small
2. Fast
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1. Setup2. Exercise3. Verify4. Teardown
The four-phase test
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My System
Unit test
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My System
SUTUnit test
Fixture
1. Setup
2. Exercise
3. Verify
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My System
Unit test 4. Teardown
1. Setup
2. Exercise
3. VerifyBoom!
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Trustworthy
Readable
Maintainable
Note: Thanks to Roy Osherove for this model
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Trustworthy
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Easy to run
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Automatically independently verified
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Same result every time
SUT
Fixture
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In memory
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test chaining
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Peter’s principle for writing unit tests:
use a minimal fresh transient
fixture per test
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use a minimal fresh transient
fixture per test
the smallest possible fixture you can get away with using
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use a minimal fresh transient
fixture per test
brand new objects every time, where you can
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use a minimal fresh transient
fixture per test
objects that are chucked after each test, left to the garbage collector
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use a minimal fresh transient
fixture per test
the test should create its own fixture
High coverage
Do TDD!
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Readable
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Well named
use a test naming convention, eg:
Method_ShouldXX()
Method_GivenXX_ShouldYY()
Method_WhenXX_ShouldYY()
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[Test]public void TestDelimitedTableNameWithSpaces(){
//...}
[Test]public void Generate_GivenTableNameWithSpaces_ShouldDelimitTableName(){
//...}
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Standardised test structure
[Test] public void Append_GivenEmptyString_ShouldNotAddToPrintItems() { // Arrange var document = CreatePrintableDocument(); // Act document.Append(""); // Assert Assert.AreEqual(0, document.PrintItems.Count); }
no teardown
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Standardised project structure
testcase class per class
test project per project
helpers and bootstrappers
keep integration tests separate
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Self-contained test
no invisible setup
no teardown
no irrelevant details
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[Test]public void TestEncryptedPassword(){ Assert.AreEqual(encryptedPassword, encryptedConfig.Password); Assert.AreEqual(encryptedPassword, encryptedConfig.DecryptedPassword); encryptedConfig.SetPrivateKey(rsa.ToXmlString(true)); Assert.AreEqual(password, encryptedConfig.DecryptedPassword);}
invisible setup
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irrelevant details
[Test]public void TestDelimitedTableNameWithSpaces(){ ClassDef.ClassDefs.Clear(); TestAutoInc.LoadClassDefWithAutoIncrementingID(); TestAutoInc bo = new TestAutoInc(); ClassDef.ClassDefs[typeof (TestAutoInc)].TableName = "test autoinc";
DeleteStatementGenerator gen = new DeleteStatementGenerator(bo, DatabaseConnection.CurrentConnection); var statementCol = gen.Generate(); ISqlStatement statement = statementCol.First(); StringAssert.Contains("`test autoinc`", statement.Statement.ToString());}
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use a minimal fresh transient
fixture per test
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Maintainable
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Be strict:
Less than 5 lines for Arrange
One line for Act
One logical Assert
Test one thing
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long, multi-phased test[Test]public void TestDeleteFlagsSetContactPerson(){ ContactPerson myContact = new ContactPerson(); Assert.IsTrue(myContact.Status.IsNew); // this object is new myContact.DateOfBirth = new DateTime(1980, 01, 20); myContact.FirstName = "Bob"; myContact.Surname = "Smith";
myContact.Save(); //save the object to the DB Assert.IsFalse(myContact.Status.IsNew); // this object is saved and thus no longer // new Assert.IsFalse(myContact.Status.IsDeleted);
IPrimaryKey id = myContact.ID; //Save the objectsID so that it can be loaded from the Database Assert.AreEqual(id, myContact.ID); myContact.MarkForDelete(); Assert.IsTrue(myContact.Status.IsDeleted); myContact.Save(); Assert.IsTrue(myContact.Status.IsDeleted); Assert.IsTrue(myContact.Status.IsNew);}
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Isolate your SUT
SUT
FixtureUnit test
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[Test]public void GetCurrentCredentialsString_ShouldReturnDeviceIDFromDeviceState(){ //Arrange var deviceState = Substitute.For<IDeviceState>(); var id = RandomValueGen.GetRandomGuid(); deviceState.GetDeviceID().Returns(id); var credentialsProvider = new CredentialsProvider(deviceState); //Act var result = credentialsProvider.GetCurrentCredentialsString(); //Assert Assert.That(result, Is.EqualTo(id.ToString()) );}
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huge fixture
[TestFixtureSetUp] public void TestFixtureSetup() { SetupDBConnection(); DeleteAllContactPersons(); ClassDef.ClassDefs.Clear(); new Car(); CreateUpdatedContactPersonTestPack(); CreateSaveContactPersonTestPack(); CreateDeletedPersonTestPack(); }
[Test] public void TestActivatorCreate() { Activator.CreateInstance(typeof (ContactPerson), true); }
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Care for your test code
Refactor and use test patterns:
• Factory method
• Custom asserts
• Fluent builders
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Test public interfaces only
“Use the front
door”
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further reading
xUnit Test Patterns: Refactoring Test CodeGerard Meszaros
The Art of Unit TestingRoy Osherove
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Working effectively with legacy codeMichael Feathers
Growing object oriented software, guided by testsSteve Freeman and Nat Pryce
even further
reading
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thanks!
@pwiles
http://
developmentthoughts.wordpress.com/http://www.chillisoft.co.za
