An automated unit testing suite gives you a number of unique advantages in comparison to other testing strategies; let us take a quick look at some of the possible reasons why unit testing tools is to be automated:

1. Automated unit testing tools fixes issues effectively as early as it can, long before the customer gets to use the software, and even before the QA team eliminates them. Most issues in new code are uncovered before now the developers/coders check code into source control. 
2. An automated unit test suite keeps watch over the code in two dimensions: space and time. In time dimension, it ensures that code written works now as well as in the future: With respect to the space dimension, the unit test that you write for some other feature guarantees the new code doesn’t infringe upon them; similarly it ensures that the coding done for other features doesn’t adversely impact the code written for this feature. 
3. Refactoring code is altering some code without affecting its behavior, whilst at the same time integrating new features to the software. Automated unit testing should be set up before refactoring or cleaning up the current code to achieve a clean code structure.
4. When you run the unit tests applying the fixes, they will uncover unwanted side-effects. Releasing quick fixes is neither the solution, nor is publishing hotfixes – only an automated unit test can reduce such things, whilst without causing new problems.
5. Automated unit testing can improve the project’s truck factor, nothing but the number of coders that if, supposing, hit by a truck would bring the project to a standstill. By improving the truck factor of the project, the developer would find it easier to take over and work on a piece of code he/she is not thoroughly familiar with. Remember if your project’s truck factor is ‘1’, then it is under higher risk.
6. Last but not least, the automated unit test brings down the need for a project’s manual testing. Though some manual testing will be required, running an automated unit testing is not only cost-effective but critical to perform the mundane testing, while the QA team can deal with the hard-to-find bugs.

The combined effects of the benefits of unit testing  & automation testing discussed above will transform the area of software engineering to be more repeatable and predictable, similar to engineering discipline, while not putting the ‘art’ in design and coding phases completely out of context. What automated unit testing can do, at best, is remove the shortcomings of the ad-hoc approach in software development which is the major reason for several problems that confront software projects.