How do you approach branch coverage for a complex conditional logic block?

Start with a decision table or a flow diagram of the conditional logic. Each binary decision (true/false, yes/no) doubles the number of branches. Three chained if-statements with no else produce 4 possible paths through the code.

For the design, work backwards from the branches you want to cover: "to reach the catch block, the API call must throw — what input causes that?" Then construct the test data that produces that condition.

Common branches that are systematically missed:

• The else of an if without an explicit else block (the implicit do-nothing case)
• Short-circuit evaluation: in A && B, if A is always true in tests, B's false case is never exercised
• Default cases in switch statements
• Exception-handling paths

For functions with more than 5–6 branches, consider whether the function should be decomposed — high cyclomatic complexity is both a test design problem and a code quality signal.