Useful design patterns for unit testing/TDD? - unit-testing

Question

Reading this question has helped me solidify some of the problems I've always had with unit-testing, TDD, et al.
Since coming across the TDD approach to development I knew that it was the right path to follow. Reading various tutorials helped me understand how to make a start, but they have always been very simplistic - not really something that one can apply to an active project. The best I've managed is writing tests around small parts of my code - things like libraries, that are used by the main app but aren't integrated in any way. While this has been useful it equates to about 5% of the code-base. There's very little out there on how to go to the next step, to help me get some tests into the main app.
Comments such as "Most code without unit tests is built with hard dependencies (i.e.'s new's all over the place) or static methods." and "...it's not rare to have a high level of coupling between classes, hard-to-configure objects inside your class [...] and so on." have made me realise that the next step is understanding how to de-couple code to make it testable.
What should I be looking at to help me do this? Is there a specific set of design patterns that I need to understand and start to implement which will allow easier testing?

Answer 1

Here Mike Clifton describes 24 test patterns from 2004. Its a useful heuristic when designing unit tests.
http://www.codeproject.com/Articles/5772/Advanced-Unit-Test-Part-V-Unit-Test-Patterns
Pass/Fail Patterns
These patterns are your first line of defence (or attack, depending on your perspective) to guarantee good code. But be warned, they are deceptive in what they tell you about the code.
The Simple-Test Pattern
The Code-Path Pattern
The Parameter-Range Pattern
Data Transaction Patterns
Data transaction patterns are a start at embracing the issues of data persistence and communication. More on this topic is discussed under "Simulation Patterns". Also, these patterns intentionally omit stress testing, for example, loading on the server. This will be discussed under "Stress-Test Patterns".
The Simple-Data-I/O Pattern
The Constraint-Data Pattern
The Rollback Pattern
Collection Management Patterns
A lot of what applications do is manage collections of information. While there are a variety of collections available to the programmer, it is important to verify (and thus document) that the code is using the correct collection. This affects ordering and constraints.
The Collection-Order Pattern
The Enumeration Pattern The
Collection-Constraint Pattern
The Collection-Indexing Pattern
Performance Patterns
Unit testing should not just be concerned with function but also with form. How efficiently does the code under test perform its function? How fast? How much memory does it use? Does it trade off data insertion for data retrieval effectively? Does it free up resources correctly? These are all things that are under the purview of unit testing. By including performance patterns in the unit test, the implementer has a goal to reach, which results in better code, a better application, and a happier customer.
The Performance-Test Pattern
Process Patterns
Unit testing is intended to test, well, units...the basic functions of the application. It can be argued that testing processes should be relegated to the acceptance test procedures, however I don't buy into this argument. A process is just a different type of unit. Testing processes with a unit tester provide the same advantages as other unit testing--it documents the way the process is intended to work and the unit tester can aid the implementer by also testing the process out of sequence, rapidly identifying potential user interface issues as well. The term "process" also includes state transitions and business rules, both of which must be validated.
The Process-Sequence Pattern
The Process-State Pattern
The Process-Rule Pattern
Simulation Patterns
Data transactions are difficult to test because they often require a preset configuration, an open connection, and/or an online device (to name a few). Mock objects can come to the rescue by simulating the database, web service, user event, connection, and/or hardware with which the code is transacting. Mock objects also have the ability to create failure conditions that are very difficult to reproduce in the real world--a lossy connection, a slow server, a failed network hub, etc.
Mock-Object Pattern
The Service-Simulation Pattern
The Bit-Error-Simulation Pattern
The Component-Simulation Pattern
Multithreading Patterns
Unit testing multithreaded applications is probably one of the most difficult things to do because you have to set up a condition that by its very nature is intended to be asynchronous and therefore non-deterministic. This topic is probably a major article in itself, so I will provide only a very generic pattern here. Furthermore, to perform many threading tests correctly, the unit tester application must itself execute tests as separate threads so that the unit tester isn't disabled when one thread ends up in a wait state
The Signalled Pattern
The Deadlock-Resolution Pattern
Stress-Test Patterns
Most applications are tested in ideal environments--the programmer is using a fast machine with little network traffic, using small datasets. The real world is very different. Before something completely breaks, the application may suffer degradation and respond poorly or with errors to the user. Unit tests that verify the code's performance under stress should be met with equal fervor (if not more) than unit tests in an ideal environment.
The Bulk-Data-Stress-Test Pattern
The Resource-Stress-Test Pattern
The Loading-Test Pattern
Presentation Layer Patterns
One of the most challenging aspects of unit testing is verifying that information is getting to the user right at the presentation layer itself and that the internal workings of the application are correctly setting presentation layer state. Often, presentation layers are entangled with business objects, data objects, and control logic. If you're planning on unit testing the presentation layer, you have to realize that a clean separation of concerns is mandatory. Part of the solution involves developing an appropriate Model-View-Controller (MVC) architecture. The MVC architecture provides a means to develop good design practices when working with the presentation layer. However, it is easily abused. A certain amount of discipline is required to ensure that you are, in fact, implementing the MVC architecture correctly, rather than just in word alone.
The View-State Test Pattern
The Model-State Test Pattern

Answer 2

I'd say you need mainly two things to test, and they go hand in hand:
Interfaces, interfaces, interfaces
dependency injection; this in conjunction with interfaces will help you swap parts at will to isolate the modules you want to test. You want to test your cron-like system that sends notifications to other services? instanciate it and substitute your real-code implementation for everything else by components obeying the correct interface but hard-wired to react in the way you want to test: mail notification? test what happens when the smtp server is down by throwing an exception
I myself haven't mastered the art of unit testing (and i'm far from it), but this is where my main efforts are going currently. The problem is that i still don't design for tests, and as a result my code has to bend backwards to accomodate...

Answer 3

Michael Feather's book Working Effectively With Legacy Code is exactly what you're looking for. He defines legacy code as 'code without tests' and talks about how to get it under test.
As with most things it's one step at a time. When you make a change or a fix try to increase the test coverage. As time goes by you'll have a more complete set of tests. It talks about techniques for reducing coupling and how to fit test pieces between application logic.
As noted in other answers dependency injection is one good way to write testable (and loosely coupled in general) code.

Answer 4

Arrange, Act, Assert is a good example of a pattern that helps you structure your testing code around particular use cases.
Here's some hypothetical C# code that demonstrates the pattern.
[TestFixture]
public class TestSomeUseCases() {
// Service we want to test
private TestableServiceImplementation service;
// IoC-injected mock of service that's needed for TestableServiceImplementation
private Mock<ISomeService> dependencyMock;
public void Arrange() {
// Create a mock of auxiliary service
dependencyMock = new Mock<ISomeService>();
dependencyMock.Setup(s => s.GetFirstNumber(It.IsAny<int>)).Return(1);
// Create a tested service and inject the mock instance
service = new TestableServiceImplementation(dependencyMock.Object);
}
public void Act() {
service.ProcessFirstNumber();
}
[SetUp]
public void Setup() {
Arrange();
Act();
}
[Test]
public void Assert_That_First_Number_Was_Processed() {
dependencyMock.Verify(d => d.GetFirstNumber(It.IsAny<int>()), Times.Exactly(1));
}
}
If you have a lot of scenarios to test, you can extract a common abstract class with concrete Arrange & Act bits (or just Arrange) and implement the remaining abstract bits & test functions in the inherited classes that group test functions.

Answer 5

Gerard Meszaros' xUnit Test Patterns: Refactoring Test Code is chock full of patterns for unit testing. I know you're looking for patterns on TDD, but I think you will find a lot of useful material in this book
The book is on safari so you can get a really good look at what's inside to see if it might be helpful:
http://my.safaribooksonline.com/9780131495050

Answer 6

have made me realise that the next step is understanding how to de-couple code to make it testable.
What should I be looking at to help me do this? Is there a specific set of design patterns that I need to understand and start to implement which will allow easier testing?
Right on! SOLID is what you are looking for (yes, really). I keep recommending these 2 ebooks, specially the one on SOLID for the issue at hand.
You also have to understand that its very hard if you are introducing unit testing to an existing code base. Unfortunately tightly coupled code is far too common. This doesn't mean not to do it, but for a good time it'll be just like you mentioned, tests will be more concentrated in small pieces.
Over time these grow into a larger scope, but it does depend on the size of the existing code base, the size of the team and how many are actually doing it instead of adding to the problem.

Answer 7

Design patterns aren't directly relevant to TDD, as they are implementation details. You shouldn't try to fit patterns into your code just because they exist, but rather they tend to appear as your code evolves. They also become useful if your code is smelly, since they help resolve such issues. Don't develop code with design patterns in mind, just write code. Then get tests passing, and refactor.

Answer 8

A lot of problems like this can be solved with proper encapsulation. Or, you might have this problem if you are mixing your concerns. Say you've got code that validates a user, validates a domain object, then saves the domain object all in one method or class. You've mixed your concerns, and you aren't going to be happy. You need to separate those concerns (authentication/authorization, business logic, persistence) so you can test them in isolation.
Design patterns help, but a lot of the exotic ones have very narrow problems to which they can be applied. Patterns like composite, command, are used often, and are simple.
The guideline is: if it is very difficult to test something, you can probably refactor it into smaller problems and test the refactored bits in isolation. So if you have a 200 line method with 5 levels of if statements and a few for-loops, you might want to break that sucker up.
So, start by seeing if you can make complicated code simpler by separating your concerns, and then see if you can make complicated code simpler by breaking it up. Of course if a design pattern jumps out at you, then go for it.

Answer 9

Dependency Injection/IoC. Also read up on dependency injection frameworks such as SpringFramework and google-guice. They also target how to write testable code.

Answer 10

Test patterns are design patterns. Both are intended to guide the construction of a piece of software.The basic test patterns that are used in software test automation are many in number and i have selected following:
"Fluent builder test pattern"
They are defined as
"A coding technique known as the "fluent builder pattern" forces the developer or test automation engineer to create the objects sequentially by invoking each setter function one at a time until all necessary properties are defined."
Fluent builder test pattern.
In the Field of Software test Automation where normally we use different automation frameworks for web based testing including Selenium, TestNG and Maven we have this test pattern. Although the fluent builder pattern isn't expressly used for unit tests but it describe how it might be useful in the organising steps. Two components make up a builder class and a number of clearly defined Set methods, each of which is in charge of changing just one aspect of the state of the produced object. In order to connect all method calls together, each of these methods returns the builder itself. A construct method uses the previously set state to create and output the objects. This Specific Test Pattern is used with a number of programming languages like C#, JAVA and Javascript. This Test Pattern is used in different testing frameworks like JUNIT, NUNIT for Asp.net.
Complex objects are a typical occurrence in our Test Scripts solutions. objects with numerous fields, each of which is challenging to construct. The Most Important Advantages of the Fluent Builder test Patterns are
1- The Code is more maintainable
2-The Code of the Automated Script is readable and simple to understand for Static reviews and Static analysis and even helpful for white box testing.
3-When you create an automated test script in any language like Java, the possibility for errors become less when you create objects for different methods.
Understanding the benefits of the builder pattern is one of the most crucial considerations you should make. As  previously stated, if we design objects that are difficult to construct, your code will be of higher quality in those situations. When an object's function Object() { [native code] } takes more than a few parameters and those parameters are objects with nested classes, you should consider using this pattern.
Fluent Builder Test Patterns in Java:
Although it appears straightforward, there is a problem. If there are too many setters methods and the object development is complicated, the Test Engineer may frequently forget to use some of the setters as they construct the object. As a result, none of the setters for many significant object attributes are being called because many of them will be null.
Missing the set property can be an expensive procedure in terms of development and maintenance for many enterprise systems' fundamental entities, such as Order or Loan, which may be begun in many different areas of the code. We make the developer call all necessary setter methods before the build function is called. 
In STLC(Software Testing Lifecycle):
We would have known that developing an automated test for an application is not particularly challenging if you were an automation engineer. Maintaining the current exams is challenging instead! When you have a large number of automated tests, that too.  you also have junior team members who are responsible for maintaining the thousands of tests suite. In STLC (Software Testing Lifecycle),
We collaborate with others. We collaborate with other QA engineers who have a variety of skill sets! It could be really challenging for some team members to comprehend the code. You might assume that they would be less productive the longer they spent trying to grasp the code. You must develop an appropriate architecture for the page objects and tests as the lead architect of the automation framework to make maintenance simple and code reusibility as well. So everyone in the STLC is familiar and have a good understanding of the framework
Try utilising the fluent builder pattern if setting up the state for multiple unit tests is a bit messy or hard. It is now very easy to read the test state. Because a single function on the builder could encapsulate a lot of state-setup code that can be written once and used by multiple tests, employing the fluent builder pattern in unit tests in some circumstances can assist to prevent code duplication.