# Coverage report

Coverage report is intended for developers using compilers GCC or Clang (including Apple Clang). It is generated by the build target `coverage_report`, which is only enabled when both `tests` and `coverage` options are set (e.g., with `-o coverage=True -o tests=True` in `conan`).

## Prerequisites

To generate the coverage report you need:

- [gcovr tool](https://gcovr.com/en/stable/getting-started.html) (can be installed e.g. with `pip install gcovr`)
- `gcov` for GCC (installed with the compiler by default)
- `llvm-cov` for Clang (installed with the compiler by default, also on Apple)
- `Debug` build type

## Creating the coverage report

The coverage report is created when the following steps are completed, in order:

1. `clio_tests` binary built with the instrumentation data, enabled by the `coverage`
   option mentioned above.
2. Completed run of unit tests, which populates coverage capture data.
3. Completed run of `gcovr` tool, which internally invokes either `gcov` or `llvm-cov`
   to assemble both instrumentation data and coverage capture data into a coverage report.

The above steps are automated into a single target `coverage_report`. The instrumented `clio_tests` binary can also be used for running regular unit tests.

In case of a spurious failure of unit tests, it is possible to re-run the `coverage_report` target without rebuilding the `clio_tests` binary (since it is simply a dependency of the coverage report target).

The default coverage report format is `html-details`, but developers can override it to any of the formats listed in `cmake/CodeCoverage.cmake` by setting `CODE_COVERAGE_REPORT_FORMAT` variable in `cmake`. For example, CI is setting this parameter to `xml` for the [codecov](https://codecov.io) integration.

After the `coverage_report` target is completed, the generated coverage report will be stored inside the build directory as either:

- A File named `coverage_report.*`, with a suitable extension for the report format.
- A Directory named `coverage_report`, with `index.html` and other files inside, for `html-details` or `html-nested` report formats.
