An attorney might be expected to examine a testimony in a number of ways. I think you would find a complete answer to your question in law books and on law websites so please go there for more details. But some of the ways would be to look at testimonies, both individually and in comparison with other testimonies and with other evidence, for relevance (irrelevance), objectivity (biases), coherence (or confusion), constency (or inconsistencies), harmony (or contradictions), the background and credibility of the witness (a professor of law, a family man, a drifter, a prostitute, a convicted forger, etc.), and so on.