Test: Due to the variability of requirements, verification is generally more complex than a single
product. For unit testing, test cases must be carefully selected and the logical way in order to minimize
the time to testing and to avoid the error of error detection. Integration Testing due to the variability
and dependencies between different products is more challenging. It should be designed carefully and
often as an iterative integrated activity. Moreover, regression testing, which is often a confusing topic
even for a single product development, becomes more complex in the product lines