Test coverage is an indirect measure of quality. It measures how well the test suite actually tests the product. Test coverage analysis helps to find out areas in the program not exercised by the test suite so that we can create additional test cases to cover those gaps. It is a structural testing technique that compares the program behavior against the apparent intention of the source code. It helps finding possible pitfalls in the structure and logic of the program.
There are two broad classifications of coverage measures – Path-based and Fault-based:
Path-based coverage: This requires the execution of a particular component of the program. For example, if the scope of the testing is limited to the payments domain alone, we design the test cases in a way that it fully exercises the payments component of the program
Fault-based coverage: This requires that the test suite exercises a program in a way that reveals all the likely faults. It is used when the test strategy is focused on finding all the defects in a feature irrespective of the components involved.
There are 6 fundamental test coverage methods as below:
Statement coverage: This reports whether each executable statement is encountered by the test suite. It is also referred to as line/segment/basic block coverage.
Decision coverage: This reports whether Boolean expressions tested in control structures are evaluated to both true and false. This is also known as branch/path coverage.
Condition coverage: This reports the true or false outcomes of each boolean sub-expressions separated by logical-OR and logical-AND if they occur
Multiple condition coverage: This reports whether every possible combination of Boolean sub-expression occurs
Function coverage: This reports whether the test suite encountered each function/procedure of the program
Call coverage: This reports whether each function call is executed