Black box testing is a software testing method that doesn’t require in-depth knowledge of the internal structre design, logic, or source code of the item being tested. Black box testing is an effective way to decide if a system’s design meets its requirements and to avoid errors in the implementation.

In this article, I will show you how black box tests can be used as functional tests.

What is black box testing?

In black box testing, the test case is derived from the specifications alone, without knowledge of the internal structure (architecture and source code) of the system under test. In other words, the point of observation (PoO) and the point of control (PoC) are solely on the externally visible behavior of the software. The system under test is therefore a black box.

Black box testing technique is often associated with requirements-based testing. It helps to decide if a system’s design meets its requirements, and to avoid errors in implementation.

In the above diagram Integration Testing, System Testing, and Acceptance Testing can be and should be tested with a black box approach.

Black box testing is the opposite of white box testing.

What is functional testing?

Functional tests are used to test how a program behaves on a user’s behalf. When designing functional tests, one needs to make sure the test cases cover the different use cases and paths. Using black box tests makes it easier to cover all possible paths and use cases.

In classical terms black box functional testing is called verification, i.e. you test the software against specification by checking the output for a given input.

Functional testing is the opposite of non-functional testing which refers to disciplines like performance, accessibility or security testing.

Overview on black box, white box, functional and non-functional testing

Be aware that you can perform integration testing with unit tests. It always depends on your definition of what an actual test really means. This matrix is meant to give you an overview of the general understanding.

Why use black box tests in functional testing?

Functional testing is a type of software testing that verifies that a system can perform its required functions. This type of testing covers the logic of the system, its user interface, and the way it reacts to various inputs.

In functional tests, black box tests can be used in a few different ways. For example, they can be used to test the user interface without requiring knowledge of the system’s internal logic. They can also be used to verify that a system handles errors properly.

Black box tests are an effective way to check if a system’s design meets its requirements and to identify errors in implementation.

There are many benefits to using black box tests in functional testing, including the fact that they’re non-intrusive and don’t require knowledge of the system’s internal logic. This makes them a valuable addition to any functional testing process.

What are the main types of black box tests?

Black box tests focus on testing the system's behavior and features and not how it works internally. For example, you could use a black box test to see how an application responds to different inputs for a given number of repetitions. This negates the need for a deep understanding of any system’s design and allows you to focus on the overall behavior of the system.

There are 6 main types of black box tests:

1. Load Testing
2. Performance Testing
3. Security Testing
4. Compatibility Testing
5. Regression Testing
6. Stress Testing

We usually summarize load, performance, and stress testing under the performance testing label.

Black box testing is used for test scenarios with high error susceptibility/probability.

How to create a test plan for a black box test?

When creating a black box test, it is important to define the input and the expected output. The input can be a number, a file, a text string, a date, a path, a logical condition, or any other input that will cause the output of the test to change. The expected output will be the content or result that is desired when input is given.

In most cases, the expected output will be a comparison of the actual output with the desired output. In order to create this comparison, you will need to compare the actual output with the expected output.

In order to create your test plan you should have these basic components:

1. The specification or requirement that you are going to test
2. The prerequisites that are required, e.g. a user is logged in
3. The inputs that you will use in your test
4. The expected output of your testFor the test report this is extended by
5. The actual output of your test
6. The result of the test
7. A list of deviations (defects) found during your test

For executing the functional tests, we add rules to these components. For example:

• The execution of a test plan creates a new revision of the corresponding test report
• A test plan is not executed if the prerequisite is not fulfilled, i.e. no test report is created
• A test report cannot be failed and have no deviations
• A test report cannot be passed and have deviations
• And so on …

Conclusion

Black box testing is an effective way to decide if a system’s design meets its requirements and to avoid errors in implementation. It does not require any knowledge of the inner logic or source code and can be performed by any tester.

The importance of functional tests is well-known. They are the most effective way to ensure that your application is working as expected. Functional tests are repeatable and should be automated with a testing tool.

Planning of black box tests is essential as the testing is only defined by input and output. To be valuable a test plan/test report structure is created which defines how the test was executed and which deviations were found.