[unit-testing] Unit test naming best practices

What are the best practices for naming unit test classes and test methods?

This was discussed on SO before, at What are some popular naming conventions for Unit Tests?

I don't know if this is a very good approach, but currently in my testing projects, I have one-to-one mappings between each production class and a test class, e.g. Product and ProductTest.

In my test classes I then have methods with the names of the methods I am testing, an underscore, and then the situation and what I expect to happen, e.g. Save_ShouldThrowExceptionWithNullName().

I think one of the most important things is be consistent in your naming convention (and agree it with other members of your team). To many times I see loads of different conventions used in the same project.

I recently came up with the following convention for naming my tests, their classes and containing projects in order to maximize their descriptivenes:

Lets say I am testing the Settings class in a project in the MyApp.Serialization namespace.

First I will create a test project with the MyApp.Serialization.Tests namespace.

Within this project and of course the namespace I will create a class called IfSettings (saved as IfSettings.cs).

Lets say I am testing the SaveStrings() method. -> I will name the test CanSaveStrings().

When I run this test it will show the following heading:

MyApp.Serialization.Tests.IfSettings.CanSaveStrings

I think this tells me very well, what it is testing.

Of course it is usefull that in English the noun "Tests" is the same as the verb "tests".

There is no limit to your creativity in naming the tests, so that we get full sentence headings for them.

Usually the Test names will have to start with a verb.

Examples include:

• Detects (e.g. DetectsInvalidUserInput)
• Throws (e.g. ThrowsOnNotFound)
• Will (e.g. WillCloseTheDatabaseAfterTheTransaction)

etc.

Another option is to use "that" instead of "if".

The latter saves me keystrokes though and describes more exactly what I am doing, since I don't know, that the tested behavior is present, but am testing if it is.

[Edit]

After using above naming convention for a little longer now, I have found, that the If prefix can be confusing, when working with interfaces. It just so happens, that the testing class IfSerializer.cs looks very similar to the interface ISerializer.cs in the "Open Files Tab". This can get very annoying when switching back and forth between the tests, the class being tested and its interface. As a result I would now choose That over If as a prefix.

Additionally I now use - only for methods in my test classes as it is not considered best practice anywhere else - the "_" to separate words in my test method names as in:

[Test] public void detects_invalid_User_Input()

I find this to be easier to read.

[End Edit]

I hope this spawns some more ideas, since I consider naming tests of great importance as it can save you a lot of time that would otherwise have been spent trying to understand what the tests are doing (e.g. after resuming a project after an extended hiatus).

Class Names. For test fixture names, I find that "Test" is quite common in the ubiquitous language of many domains. For example, in an engineering domain: StressTest, and in a cosmetics domain: SkinTest. Sorry to disagree with Kent, but using "Test" in my test fixtures (StressTestTest?) is confusing.

"Unit" is also used a lot in domains. E.g. MeasurementUnit. Is a class called MeasurementUnitTest a test of "Measurement" or "MeasurementUnit"?

Therefore I like to use the "Qa" prefix for all my test classes. E.g. QaSkinTest and QaMeasurementUnit. It is never confused with domain objects, and using a prefix rather than a suffix means that all the test fixtures live together visually (useful if you have fakes or other support classes in your test project)

Namespaces. I work in C# and I keep my test classes in the same namespace as the class they are testing. It is more convenient than having separate test namespaces. Of course, the test classes are in a different project.

Test method names. I like to name my methods WhenXXX_ExpectYYY. It makes the precondition clear, and helps with automated documentation (a la TestDox). This is similar to the advice on the Google testing blog, but with more separation of preconditions and expectations. For example:

WhenDivisorIsNonZero_ExpectDivisionResult
WhenDivisorIsZero_ExpectError
WhenInventoryIsBelowOrderQty_ExpectBackOrder
WhenInventoryIsAboveOrderQty_ExpectReducedInventory

I use Given-When-Then concept. Take a look at this short article http://cakebaker.42dh.com/2009/05/28/given-when-then/. Article describes this concept in terms of BDD, but you can use it in TDD as well without any changes.

I like to follow the "Should" naming standard for tests while naming the test fixture after the unit under test (i.e. the class).

To illustrate (using C# and NUnit):

[TestFixture]
public class BankAccountTests
{
  [Test]
  public void Should_Increase_Balance_When_Deposit_Is_Made()
  {
     var bankAccount = new BankAccount();
     bankAccount.Deposit(100);
     Assert.That(bankAccount.Balance, Is.EqualTo(100));
  }
}

Why "Should"?

I find that it forces the test writers to name the test with a sentence along the lines of "Should [be in some state] [after/before/when] [action takes place]"

Yes, writing "Should" everywhere does get a bit repetitive, but as I said it forces writers to think in the correct way (so can be good for novices). Plus it generally results in a readable English test name.

Update:

I've noticed that Jimmy Bogard is also a fan of 'should' and even has a unit test library called Should.

Update (4 years later...)

For those interested, my approach to naming tests has evolved over the years. One of the issues with the Should pattern I describe above as its not easy to know at a glance which method is under test. For OOP I think it makes more sense to start the test name with the method under test. For a well designed class this should result in readable test method names. I now use a format similar to <method>_Should<expected>_When<condition>. Obviously depending on the context you may want to substitute the Should/When verbs for something more appropriate. Example: Deposit_ShouldIncreaseBalance_WhenGivenPositiveValue()

I like this naming style:

OrdersShouldBeCreated();
OrdersWithNoProductsShouldFail();

and so on. It makes really clear to a non-tester what the problem is.

the name of the the test case for class Foo should be FooTestCase or something like it (FooIntegrationTestCase or FooAcceptanceTestCase) - since it is a test case. see http://xunitpatterns.com/ for some standard naming conventions like test, test case, test fixture, test method, etc.

In VS + NUnit I usually create folders in my project to group functional tests together. Then I create unit test fixture classes and name them after the type of functionality I'm testing. The [Test] methods are named along the lines of Can_add_user_to_domain:

- MyUnitTestProject   
  + FTPServerTests <- Folder
   + UserManagerTests <- Test Fixture Class
     - Can_add_user_to_domain  <- Test methods
     - Can_delete_user_from_domain
     - Can_reset_password

I should add that the keeping your tests in the same package but in a parallel directory to the source being tested eliminates the bloat of the code once your ready to deploy it without having to do a bunch of exclude patterns.

I personally like the best practices described in "JUnit Pocket Guide" ... it's hard to beat a book written by the co-author of JUnit!

Kent Beck suggests:

• One test fixture per 'unit' (class of your program). Test fixtures are classes themselves. The test fixture name should be:

  [name of your 'unit']Tests
  

• Test cases (the test fixture methods) have names like:

  test[feature being tested]
  

For example, having the following class:

class Person {
    int calculateAge() { ... }

    // other methods and properties
}

A test fixture would be:

class PersonTests {

    testAgeCalculationWithNoBirthDate() { ... }

    // or

    testCalculateAge() { ... }
}

See: http://googletesting.blogspot.com/2007/02/tott-naming-unit-tests-responsibly.html

For test method names, I personally find using verbose and self-documented names very useful (alongside Javadoc comments that further explain what the test is doing).