Testing and debugging are two of the most common processes found in development teams. At first glance, they may appear similar, but they are indeed quite different. Testing is finding defects while debugging is locating their cause in the code and fixing them. Let's look at each in detail.

What is Testing?

Testing is carried out by testers either by executing test cases or by ad hoc testing. The main objective of testing is to find defects in the software. The tester does functional testing to search flaws in the end-user functionality and non-functional testing to find faults in operational areas like performance and security. Testing can also happen at different levels - unit testing, integration testing, system testing, and acceptance testing - with the overall strategy to find bugs as early as possible.

The output of testing is a defect report. This report lists the exact steps to duplicate the defect so that developers can locate the source of the bug and fix it.

Let's take a real-world example - testers find that a particular user cannot log in to their test application. They file a defect report that mentions the URL of the test application, the username, the password, and the browser details.

They also found another bug that could create two accounts with the same usernames but different cases, such as Jack and jack.

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What is Debugging?

Debugging, done by developers, is a process of finding and fixing the cause of a bug. They often use a debugger tool to help them step line-by-line through the source code. A debugger also allows developers to examine variables and evaluate expressions, thus enabling them to locate the problem quickly.

Continuing with the above example, the developer finds that the login fails because the search for users was case-sensitive during debugging. For example, the search for a user with the username 'Jack' would not return users with the username 'jack'.

They also realized that this was also the exact reason for the other bug. Fixing the search would also solve this problem.

Testing and Debugging Compared

Objective The objective of testing is to identify defects in the application. The purpose of debugging is to fix errors observed in testing.
Process It is the process to identify the failure of code. It is the process of fixing mistakes in the code.
Programming Knowledge Most testing requires no knowledge of the source code. Debugging requires a proper understanding of the source code.
Performed By A tester performs testing. Testing can be carried out both by insiders and by outsiders. Debugging is performed by a programmer. Only an insider does the debugging.
Design Knowledge Design knowledge is not needed in the testing process. Design knowledge is not needed but recommended as haphazardly fixing bugs can cause other defects or maintenance problems in the future.
Automation Testing can be manual or automated. Debugging is always manual.
Initiation Testers can only initiate testing after developers write the code. Debugging begins after a failed test case execution.