Black Box Testing

Black Box Testing - All programs work on some set of inputs and create some set of outputs. Black box testing looks at the program's inputs and outputs rather than the internal lines of code.

Black box testing implies that your program is literally a black box. You are not concerned with its inner workings. All you know is that when you give it a certain set of inputs, it gives back a certain set of outputs.

This is true whether the program is a report, a webpage, or an internal calculating procedure. Note that the unit testing is almost always done by the original programmer.

So, although black box testing implies that you do not know the interior workings of the program, the original developer obviously will.

This can make it more difficult to do black box testing since the original programmer may have certain biases in his or her understanding of the component that may influence how they conduct the testing.

However, even given the potential biases and assumptions, this type of testing is still fundamental to a good unit test. An example of black box testing is a webpage that takes a numeric employee ID and returns your name, address, and telephone number.

You can generate three test cases to test this requirement

  1. First, test with a valid numeric employee id.
  2. Second, test with an invalid numeric id.
  3. Then enter an employee id with alphas.

Theoretically, you could enter test cases for all valid employee ids, and you could test with an infinite number of invalid ids. However, you do not need all of them.

Three test cases for this particular example should result in proper test coverage. Another aspect of black box testing is to test at the boundaries to see if the requirement includes a valid range of input.

For instance, if a certain field can hold a number from one to a hundred, you want to test at the boundaries of the range. So, you could create five test cases of 1, 100 (the boundaries), 0, 101 (just out of bounds) and an alpha character.

Again, although there are an infinite number of test cases possible, those five should suffice.

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