# Inconsistent VM behavior in sway unit tests **URL:** \ **Category:** Sway\ **Created:** [February 1, 2023, 12:38am UTC](https://forum.fuel.network/t/inconsistent-vm-behavior-in-sway-unit-tests/1742 "2023-02-01T00:38:32Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![rsproule](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.fuel.network/rsproule/32/987_2.png) [@rsproule](https://forum.fuel.network/u/rsproule)\ **Post date:** [February 1, 2023, 12:38am UTC](https://forum.fuel.network/t/inconsistent-vm-behavior-in-sway-unit-tests/1742/1 "2023-02-01T00:38:32Z")
I have been writing some unit tests in sway via the `#[test]` annotation feature. There seems to be some inconsistency in the runtime of these tests compared to running normal scripts via the SDK. Specifically, I noticed this bug while I was building a library that uses the [signed integers from sway libs](https://github.com/FuelLabs/sway-libs/tree/f33fc23bdfd4b57e6be31c43de7181899bf0d28c/libs/signed_integers). In the sway unit tests, the VM panics and fails the test for any standard math operations on the `I64` type. I was able to reproduce this inside of the sway libs repo by adding a simple test to any of the signed integer libraries. This [commit](https://github.com/FuelLabs/sway-libs/compare/master...rsproule:sway-libs-demo-unit-test-bug:master) demonstrates this in a forked repo. ```auto #[test] fn test_add() { // note this is identical code from the tests in `../../tests/src/signed_integers/signed_i64/src/main.sw` // this should not fail, but does if you run `forc test` in this dir let one = I64::from(1u64); let mut res = one + I64::from(1u64); assert(res == I64::from(2u64)); } ``` forc test: ```auto Bytecode size is 316 bytes. Running 2 tests test test_add ... FAILED (570.375µs) test test_nothing ... ok (58.166µs) failures: - test test_add, "/Users/someguy/code-for-reading/sway-libs-demo-unit-test-bug/libs/signed_integers/src/i64.sw":162 Result: FAILED. 1 passed. 1 failed. Finished in 628.541µs. ``` fuelup show: ```auto Default host: aarch64-apple-darwin fuelup home: /Users/someguy/.fuelup installed toolchains -------------------- latest-aarch64-apple-darwin (default) active toolchain ----------------- latest-aarch64-apple-darwin (default) forc : 0.33.1 - forc-client - forc-deploy : 0.33.1 - forc-run : 0.33.1 - forc-doc : 0.33.1 - forc-explore : 0.28.1 - forc-fmt : 0.33.1 - forc-index : 0.2.1 - forc-lsp : 0.33.1 - forc-wallet : 0.1.3 fuel-core : 0.16.1 fuel-indexer : 0.2.0 ``` ---
**Author:** ![mindtree](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.fuel.network/mindtree/32/5_2.png) [@mindtree](https://forum.fuel.network/u/mindtree)\ **Post date:** [February 1, 2023, 1:26am UTC](https://forum.fuel.network/t/inconsistent-vm-behavior-in-sway-unit-tests/1742/2 "2023-02-01T01:26:59Z")
Thanks for the report and for digging in! Forc’s testing functionality is brand new so feedback is appreciated 🙏 > fuelup show: Could you confirm that you’re getting the same behaviour on the `fuelup` nightly toolchain too? And could you also share the version of the Rust SDK that you’re using to run your script that works? For some added context: `forc test` works by running its own unique instance of the Fuel VM interpreter for each `#[test]`. In theory, executing with it _should_ be the same as executing the script on a freshly spawned local fuel-core node, though without the indirection of networking calls etc. We should at least be outputting the revert code and an associated message on failure too - I’ll open an issue at the Sway repo for this as a high priority. ---
**Author:** ![mindtree](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.fuel.network/mindtree/32/5_2.png) [@mindtree](https://forum.fuel.network/u/mindtree)\ **Post date:** [February 1, 2023, 1:38am UTC](https://forum.fuel.network/t/inconsistent-vm-behavior-in-sway-unit-tests/1742/3 "2023-02-01T01:38:14Z")
Oh also - can you try running `forc test` with the new raw log output? E.g. ```plaintext forc test --log --pretty-print ``` This will dump the raw logs from the receipt that might help to debug what’s going on. ---
**Author:** ![rsproule](https://sea2.discourse-cdn.com/flex022/user_avatar/forum.fuel.network/rsproule/32/987_2.png) [@rsproule](https://forum.fuel.network/u/rsproule)\ **Post date:** [February 1, 2023, 5:23am UTC](https://forum.fuel.network/t/inconsistent-vm-behavior-in-sway-unit-tests/1742/4 "2023-02-01T05:23:36Z")
switched back over to nightly ```auto ❯ fuelup show Default host: aarch64-apple-darwin fuelup home: /Users/someguy/.fuelup installed toolchains -------------------- latest-aarch64-apple-darwin nightly-aarch64-apple-darwin (default) active toolchain ----------------- nightly-aarch64-apple-darwin (default) forc : 0.33.1+nightly.20230201.b6cd10ba9d - forc-client - forc-deploy : 0.33.1+nightly.20230201.b6cd10ba9d - forc-run : 0.33.1+nightly.20230201.b6cd10ba9d - forc-doc : 0.33.1+nightly.20230201.b6cd10ba9d - forc-explore : 0.28.1+nightly.20230201.4bb7392eed - forc-fmt : 0.33.1+nightly.20230201.b6cd10ba9d - forc-index - not found - forc-lsp : 0.33.1+nightly.20230201.b6cd10ba9d - forc-wallet : 0.1.3+nightly.20230201.543bc1f4d7 fuel-core : 0.16.1+nightly.20230201.d761d2b4bb fuel-indexer - not found ``` and the the logs look empty: ```auto ❯ forc test --logs --pretty-print WARNING! unused manifest key: project.target WARNING! unused manifest key: project.target Compiled library "core". Compiled library "std". Compiled library "signed_integers". Bytecode size is 316 bytes. Running 2 tests test test_add ... FAILED (119.167µs) [] test test_nothing ... ok (44.416µs) [] failures: - test test_add, "/Users/someguy/code-for-reading/sway-libs-demo-unit-test-bug/libs/signed_integers/src/i64.sw":162 Result: FAILED. 1 passed. 1 failed. Finished in 163.583µs. ```