Loop testing - a white box testing technique and types of loop testing.

Loop testing is a kind of white box testing technique that focuses exclusively on the validity of loop constructs. Four classes of loops can be defined: Simple loops, Concatenated loops, Nested loops, and unstructured loops.

- Simple Loops: The following sets of tests can be applied to simple loops, where 'n' is the maximum number of allowable passes through the loop.
a) Skip the loop entirely.
b) Only one pass through the loop.
c) Two passes through the loop.
d) 'm' passes through the loop where m < n.
e) n-1,n,n+1 passes through the loop.

- Nested Loops: If we extend the test approach from simple loops to nested loops, the number of possible tests would grow geometrically as the level of nesting increases.
a) Start at the innermost loop. Set all other loops to minimum values.
b) Conduct simple loop tests for the innermost loop while holding the outer loops at their minimum iteration parameter values. Add other tests for out-of-range or exclude values.
c) Work outward, conducting tests for the next loop, but keep all other outer loops at minimum values and other nested loops to typical values.
d) Continue until all loops have been tested.

- Concatenated Loops: These loops can be tested using the approach defined for simple loops,If each of these loops is independent of the other. However, if two loops are concatenated and the loop counter for loop one is used as the initial value for loop two, then the loops are not independent.

- Unstructured Loops: Whenever possible, this class of loops should be redesigned to reflect the use of the structured programming constructs.