At a high level, you can break down testing into two significant categories: Black Box Testing and White Box Testing. The fundamental difference lies in the preparation and applicability of test cases: Black Box testing allows for early test case preparation based on specifications, while White Box testing requires the software's design or code to be available for test case development. The difference and importance of these two types of testing are things you must know when entering the QA field.

The important thing is not to stop questioning. Curiosity has its own reason for existing.- Albert Einstein -

Black Box Testing

Black Box Testing is when you run tests without knowing or having access to the application's internals; this includes the internal structure, design, and implementation. When testing, you are observing the behavior of the software. You are considering whether the software performs as expected in scenarios typical of an end user's interactions.

Black box testing is effective in detecting discrepancies between the software's actual functionality and its specified requirements, making it a critical component of quality assurance processes.

Testing Levels Applied to Black Box Testing

Thanks to Black box testing's versatility, it applies to nearly every level of testing within the software development lifecycle. Testing across these levels ensures the software meets requirements and user expectations.

Here are the primary levels:

Unit Testing:
At this level, black box testing can be applied to individual components or units to validate their functionality against specified requirements. Although people often associate unit testing with white box techniques, testers can also employ black box approaches, particularly for testing APIs or service interfaces.
Integration Testing:
This level tests the interfaces and interactions between components or systems. We use Black Box testing methods to verify that the different parts of the application work together as expected.
System Testing:
We test the application's system at this level to ensure it meets requirements. We evaluate the system's overall behavior, functionality, and performance through black box testing, guaranteeing alignment with requirements and user expectations.
Acceptance Testing:
In this final level, we test the software in an actual or simulated(staging, development, local, etc) environment to confirm it meets the acceptance criteria the client or end-users established. Here, black box testing techniques are crucial, focusing on the user experience and ensuring the software performs its intended functions effectively in real-world scenarios.

Black Box Testing Techniques

These techniques ensure software behaves as expected, based on its requirements and without delving into the internals.

Here are the key techniques:

Equivalence Partitioning:
This technique actively divides input data into partitions of equivalent data, from which we derive test cases. We assume that the software will treat all values within a partition identically.
Boundary Value Analysis:
Targets the boundary values of input data partitions, testing the edges between these partitions. We test the minimum and maximum values at these edges, ensuring comprehensive coverage.
Decision Table Testing:
Useful for functions with logical conditions. It systematically identifies test cases by listing all possible conditions and actions in a tabular form.
State Transition Testing:
Based on state transition diagrams. This technique tests the various states an application can be in and validates the transitions between these states based on triggering events.

Black Box Advantages and Disadvantages

Now that you have a general understanding of Black Box Testing let's look at some of the advantages and disadvantages of this approach.

Advantages

Very productive when testing large segments of code
No need for access to the code
Provides separation between user and developer perspectives
User-Centric Approach

Disadvantages

Testing coverage can be limited
Tests can become inefficient or not provide a good return on investment due to the Tester's lack of knowledge about software internals
Potential for Redundancy

White Box Testing

White Box testing, sometimes called 'clear' or 'glass' box testing, is the opposite of black box testing. This approach demands understanding the software's code, structure, and implementation. We can use this inside information to design test cases, identify potential paths through the software, and ensure thorough testing of those pathways.

This method allows for a thorough examination of the software, identifying issues related to the internal structure that might not be visible from the outside.

Testing Levels Applied to White Box Testing

White Box testing techniques are applicable across various levels of testing, from the most granular level of Unit Testing to more comprehensive tests that examine the interactions between different parts of the software. While it shares some of these levels with Black Box testing, the application method distinguishes them.

Here are the primary levels:

Unit Testing:
The most common level for white-box testing, focusing on the function or method level. Testers write test cases covering every possible path through a code unit.
System Testing:
Even though it's less common at this level, we can apply white-box testing to examine the interactions within the entire system. This approach becomes especially critical in complex systems where a deep understanding of the internal workings is essential for testing.
API Testing:
In this specific type of integration testing, we actively use white-box techniques to test direct calls to the application's API. Thus ensuring that they perform as expected under various conditions.

White Box testing's detailed approach to examining the internal structures of software makes it an invaluable tool, ensuring that the code functions correctly from an external perspective and is logically sound and well-structured internally.

White Box Testing Techniques

It is essential to take a structured approach to analyze and test the internal structure and logic of the software code. These techniques enable testers to ensure that the code behaves as expected under various conditions and that all possible paths and branches are executed at least once, thereby identifying hidden errors.

Here are the primary test techniques:

Statement Testing:
Aims to execute all statements in the code at least once. This technique focuses on achieving a high level of coverage regarding the lines of code executed during the test.
Branch Testing:
Expands on statement testing by ensuring execution of every possible branch from each decision point. We test the true and false outcomes of decisions, covering all potential pathways.

White Box Advantages and Disadvantages

Now that we've had an overview of White Box Testing, it's time to look at some of the advantages and disadvantages of this approach.