The problem

When running tests for Shopify Functions with cargo test, they sporadically fail with out of bounds errors:

~/cargo/registry/src/index.crates.io-6f17d22bba15001f/shopify_function_provider-1.0.1/src/string_interner.rs:26:39:
index out of bounds: the len is 81 but the index is 84
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

This does not happen when running a single test or when running the tests with a single thread (via cargo test -- --test-threads=1), so there is seemingly a race condition.

The specific function we were experiencing issues with can be found in my PR where I also update calls to cargo test to use --test-threads=1 to work around this issue temporarily. The issue should be easy to reproduce when running tests for that function.