Code Coverage

Measuring code coverage uses tools to identify lines of code that are and aren't executed by tests. Code coverage stats can give us an idea of how much of a contract is actually tested by its tests.

tip

Mutation testing is another form of coverage testing. See Mutation Testing.

In rust projects the cargo-llvm-cov tool can be used to generate coverage stats, HTML reports, and lcov files that IDEs will load to display the coverage in the code editor.

Install cargo-llvm-cov before proceeding with the other commands.

cargo install cargo-llvm-cov

How to Get Coverage Stats

Run the test subcommand that will run the tests and output the stats per file.

cargo llvm-cov test

How to Generate a Coverage Report with Code

Run the test subcommand that will run the tests and output a set of HTML files showing which lines of code are covered.

cargo llvm-cov test --html --open

The output of the command will indicate where the HTML file has been written. Open the file in a browser.

How to Generate an LCOV File for IDEs

Run the test subcommand that will run the tests and output a single lcov.info file.

cargo llvm-cov test --lcov --output-path=lcov.info

Load the lcov.info file into your IDE using it's coverage feature. In VSCode this can be done by installing the Coverage Gutters extension and executing the Coverage Gutters: Watch command.

info

Measuring code coverage in fuzz tests requires different tooling. See Fuzzing.