Unit Testing Concepts

So you've built some software but before you want to release it to the end users, you are not sure if there are any major bugs, so you will need to test it! This is where Unit Testing comes in!

Unit Testing is a level of software testing where individual units / components of a software are tested. The purpose is to validate that each unit of the software performs as designed. A unit is the smallest testable part of any software. It usually has one or a few inputs and usually a single output. In procedural programming, a unit may be an individual program, function, procedure, etc. In OO Programming, the smallest unit is a method, which may belong to a base / super class, abstract class or a derived / child class. (Some treat a module of an application as a unit. This is to be discouraged as there will probably be many individual units within that module.) Unit testing frameworks, drivers, stubs, and mock / fake objects are used to assist in unit testing.

Unit Testing in reference to other Testing methods

Method

The Unit Testing Method is performed by using the White Box Testing method.

White Box Testing is a analysis of the internal structure of the component or system. We can derive test cases and / or select test cases based on an analysis of the internal structure of a component or system.

For example, the tester could examine the code to see why the program is not running as expected, but does not write code for testing.

Now, back to Unit Testing, it is the first level of software testing and is performed prior to Integration Testing.

Who performs it? It is normally performed by software developers themselves or their peers. In rare cases, it may also be performed by independent software testers.

Tasks

Unit Testing consists of various tasks, usually one would have to prepare the tests, then review and rework. Then the Test cases / scripts come into play, which involves the same sub tasks are mentioned previously, and then the Unit Test is performed.

Benefits

Unit Testing increases confidence in changing / maintainig code. If good unit tests are written and if they are run every time any code is changed, we will be able to promptly catch any defects introduced due to the change. Also, if codes are already made less interdependent to make unit testing possible, the unintended impact of changes to any code is less.

Codes are more reusable In order to make unit testing possible, codes need to be modular. This means that codes are easier to reuse.

Development is faster. How? Code that doesn't get Unit Tested usually ends up being tested in non-organised ways, such as placing breakpoints anywhere in the code to test it. Code that is tested by the Unit Testing route tends to be tested well and on average is quicker and more efficient than the non-organised tests.

The cost of fixing a defect detected during unit testing is lesser in comparison to that of defects detected at higher levels Compare the cost of a defect detected during acceptace testing or when the software is live.

Debugging is easy. When a test fails, the only code that need to be debugged are the changes. With testing at higher levels, changes made over the spa of several days / weeks / months nee to be scanned.

Codes are more reliable Self explanatory.

Tips

Find a tool / framework for your language
Do not create test cases for everything. Instead, focus on the tests that impact the behaviour of the system.
Isolate the development environment from the test environment
Use test data that is close to that of production
Before fixing a defect, write test code that exposes the defect. This is because you will later be able to catch the defet if you do not fix it properly.
Write test caes that are independent of each other. For example, if a class depends on a database, do not write a case that interacts with the database to test the class. Instead, create an abstract interface around that database connection and implement that interface with a mock object.
Aim at covering all paths through the unit. Pay particular attention to loop conditions.
Make sure you are using a version control system to keep track of your test scripts.
In addition to writing cases to verify the behaviour, write cases to ensure the performance of the code.
Perform unit tests continuously and frequently.

Sources: (click on them to see them)