Types of code coverage in the IDE
Several types of metrics are commonly used in commercial code-coverage tools, ranging from simple line or block coverage (i.e. this statement was executed) to condition-decision coverage (i.e. all terms in this Boolean expression are exercised). A given tool usually provides a combination of types.
The coverage tool in the IDE is a visual front end to the gcov metrics produced by the gcc compiler. These coverage metrics are essentially basic block coverage and branch coverage.
The IDE presents these metrics as line coverage, showing which lines are fully covered, partially covered, and not covered at all. The IDE also presents percentages of coverage in terms of the actual code covered (i.e. not just lines).
Block coverage, sometimes known as line coverage, describes whether a block of code, defined as not having any branch point within (i.e. the path of execution enters from the beginning and exits at the end) is executed or not.
By tracking the number of times the block of code has been executed, the IDE can determine the total coverage of a particular file or function. The tool also uses this information to show line coverage by analyzing the blocks on each line and determining the level of coverage of each.
Branch coverage can track the path of execution taken between blocks of code. Although this metric is produced by the gcc compiler, currently the IDE doesn't provide this information.