> ## Documentation Index
> Fetch the complete documentation index at: https://developers.stellar.org/llms.txt
> Use this file to discover all available pages before exploring further.

# Code Coverage

> Code coverage tools find code not tested.

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 its coverage feature. In VSCode this can be done by installing the [Coverage Gutters] extension and executing the `Coverage Gutters: Watch` command.

> [!NOTE]
>
> Measuring code coverage in fuzz tests requires different tooling. See \[Fuzzing].

[Coverage Gutters]: https://marketplace.visualstudio.com/items?itemName=ryanluker.vscode-coverage-gutters

[Mutation Testing]: https://developers.stellar.org/docs/build/guides/testing/mutation-testing.md

[Fuzzing]: https://developers.stellar.org/docs/build/guides/testing/fuzzing.md