Unit Testing

Once we’ve written a program, how can we verify that it works correctly? There are many ways to do this, but one of the most common is unit testing.

Unit Testing

Unit testing a program involves writing code that actually runs the program and verifies that it works correctly. In addition, many unit tests will also check that the program produces appropriate errors when given bad input, or even that it won’t crash when given invalid input.

For example, a simple unit test for the maximum() method would be:

function MAXIMUMTEST()
    ARRAY = new array[5]
    ARRAY[0] = 5
    ARRAY[1] = 25
    ARRAY[2] = 10
    ARRAY[3] = 15
    ARRAY[4] = 0
    RESULT = MAXIMUM(ARRAY)
    if RESULT == 25:
        print "Test Passed"
    end if
end function

This code will simply create an array that we know the maximum value of, and then confirm that our own maximum() method will find the correct result.

Of course, this is a very simplistic unit test, and it would take several more unit tests to fully confirm that the maximum() method works completely correctly.

However, it is important to understand how this test relates to the preconditions and postconditions that were established on previous pages. Here, the unit tests creates a variable ARRAY which is an array of at least one numerical value. Therefore, it has met the preconditions for the maximum() method, so we can assume that if maximum() is written correctly, then the postconditions will be true once it is has executed. This is the key assumption behind unit tests.