Update testing guide with code coverage for fuzzing

docs/build/guides/testing/code-coverage.mdx

@@ -49,5 +49,12 @@ 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].
+
+:::
+
 [Coverage Gutters]: https://marketplace.visualstudio.com/items?itemName=ryanluker.vscode-coverage-gutters
 [Mutation Testing]: mutation-testing.mdx
+[Fuzzing]: fuzzing.mdx

docs/build/guides/testing/fuzzing.mdx

@@ -116,6 +116,47 @@ There is another tool for fuzzing Rust code, `cargo-afl`. See the [Rust Fuzz boo
 
 :::
 
+### How to Get Code Coverage of Fuzz Tests
+
+Getting code coverage data for fuzz tests requires some different tooling than when doing the same for regular Rust tests.
+
+1. Run the fuzz tests until it has produced a corpus, just as in step 7 above.
+
+   ```
+   cargo +nightly fuzz run --sanitizer thread fuzz_target_1
+   ```
+
+2. Install the llvm-tools for the nightly compiler.
+
+   ```
+   rustup component add --toolchain nightly llvm-tools-preview
+   ```
+
+3. Run the fuzz coverage command that'll execute the corpus and write coverage data to the coverage directory in the `profdata` format.
+
+   ```
+   cargo +nightly fuzz coverage --sanitizer thread fuzz_target_1
+   ```
+
+4. Run the llvm-cov command to convert the profdata file to an lcov file.
+
+   ```
+   LLVM_TOOLS_PATH=$(dirname $(find $(rustc +nightly --print sysroot) -name 'llvm-cov'))
+   $LLVM_TOOLS_PATH/llvm-cov export -instr-profile=fuzz/coverage/fuzz_target_1/coverage.profdata \
+       -format=lcov \
+       -object target/aarch64-apple-darwin/coverage/aarch64-apple-darwin/release/fuzz_target_1 \
+       --ignore-filename-regex "rustc" > 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.
+
+:::tip
+
+To measure code coverage of regular Rust tests, see [Code Coverage].
+
+:::
+
+
 [increment example]: https://github.com/stellar/soroban-examples/blob/main/increment/src/lib.rs
 [Differential Testing with Test Snapshots]: ./differential-tests-with-test-snapshots.mdx
 [stellar contract fetch]: ../../../tools/developer-tools/cli/stellar-cli.mdx#stellar-contract-fetch
@@ -124,3 +165,5 @@ There is another tool for fuzzing Rust code, `cargo-afl`. See the [Rust Fuzz boo
 [stellar/rs-soroban-sdk#1360]: https://github.com/stellar/rs-soroban-sdk/issues/1360
 [fuzzing example]: ../../smart-contracts/example-contracts/fuzzing.mdx
 [Rust Fuzz Book]: https://rust-fuzz.github.io/book
+[Code Coverage]: code-coverage.mdx
+[Coverage Gutters]: https://marketplace.visualstudio.com/items?itemName=ryanluker.vscode-coverage-gutters