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The Top Black Box Testing Techniques

Ready to refresh your knowledge of the top testing techniques? Black box testing refers to a whole treasure trove of software testing techniques that help us achieve excellent test coverage while narrowing the number of cases and saving time.

Read on to understand what black box testing is (exactly) and the techniques your team can use to impact your next cycle.

What is black box testing?

Black box testing simply means that the internal working structure (the code) is unknown. The testers validate the functional requirements without reviewing the source code.

Think of the code as being hidden inside of a black box. For all inputs, the tester compares the expected outputs with the actual outputs.

black box testing and testlio

With this type of testing, testers don’t review the internal code and don’t necessarily have knowledge of its structure or internal paths. Instead, they use knowledge of the software requirements to formulate test cases.

Black box vs. white box testing?

If black box testing represents “unknown” internal software, then think of white box testing as “known.”

With white box testing, a tester must have knowledge of the programming language and system structure being used. Unlike black box testing, which relies on the perspective of an end-user, white box testing includes techniques that an end user would never simulate because testers are reviewing the code to find issues with security, information flow and speed.

What are the top black box testing techniques?

Black box testing techniques are simply all of the testing techniques in which the tester is not required to know the internal code.

There are many.

These six black box testing techniques aim to strategically cover the product while lowering the total amount of cases:

  • Equivalence partitioning – This black box testing example reduces tons of rework. Testers group test conditions together so that in each group, only one test condition requires testing. If that condition works, then all of that group’s conditions must work also. For example, with an uploader, this technique can be used to test file types and sizes without having to overlap every combination.  
  • Boundary value analysis – With boundary value analysis, you test the boundaries of what values are allowed. So, if the system should only accept a number between 1 and 100, you will want to test those boundaries, as well as just over and just under (0 and 101) but you will not need to waste time testing the numbers in between.
  • Decision table testing – This technique is best used for complex combinations, where various inputs lead to different decisions (unlike equivalence partitioning and boundary value analysis). Also known as cause and effect tables, decision tables can help clarify expected outputs and make sure no combinations are missed when forming test cases.
black box testing example of decision testing
  • State transition testing – Any system that can give different outputs for the same input depending on outside conditions requires state transition testing. For example: an ATM machine that gives the tester $60 and then later doesn’t give the tester $60 (because the account has dipped below that amount); or a traffic light that turns green when you trigger the sensor, but later doesn’t (because someone else was there first and is allowed to turn left before you go straight). This type of black box test example can have the same inputs but different outputs, because the system has “transitioned” to a new state.
  • Exploratory testing – With exploratory testing, the tester is closely simulating user behavior while strategically moving through actions in the system to maximize test coverage. This is considered a black box technique because no knowledge of the internal code is required. Instead, testers need to know the software requirements and expected behaviors. From there, they can behave like users—but always keeping their testers’ hats on.
  • Error guessing – Error guessing is just like it sounds. A tester “guesses” were errors are most likely to be found. But since the following factors go into the decision, a “guess” isn’t really a fair term: the testers’ own experience, knowledge of the application, results from previous test cycles, customer issue tickets, issues with previous releases, and risk reports. When trying to choose which part of the application will receive the most thorough testing, error guessing is a must.  

Benefits of black box testing techniques

This form of testing can be done using record and playback tools, but do not require any costly tools or suites.

The key with black box testing is to strategize test plan coverage, overlap test cases where needed, reduce redundancy where possible, and combine techniques to minimize the number of bugs that make it to production.

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