# `defmt-test`
`defmt-test` is a test harness for embedded devices that lets you write and run unit tests *on your device* as if you were using the built-in `#[test]` attribute.
It is compatible with [rust-analyzer]'s `▶ Run Test` button, which means you can flash and run your tests straight from VS Code:
For a full list of defmt-test's capabilities, please refer to the documentation below.
[rust-analyzer]: https://rust-analyzer.github.io
## Using `defmt-test` in a new project
We suggest you start from the [`app-template`].
From there you can execute `cargo test --lib` to run library unit tests, i.e. `#[test]` functions in the library crate (`src/lib.rs`).
[`app-template`]: https://github.com/knurling-rs/app-template
``` console
$ cargo test --lib
(..)
(1/1) running `it_works`...
└─ app::unit_tests::__defmt_test_entry @ src/lib.rs:33
all tests passed!
└─ app::unit_tests::__defmt_test_entry @ src/lib.rs:28
(..)
(HOST) INFO device halted without error
```
And execute `cargo test --test integration` to run integration tests, i.e. the `tests/integration.rs` file.
``` console
$ cargo test --test integration
(..)
0.000000 INFO (1/2) running `assert_true`...
└─ test::tests::__defmt_test_entry @ tests/test.rs:7
0.000001 INFO (2/2) running `assert_false`...
└─ test::tests::__defmt_test_entry @ tests/test.rs:7
0.000002 ERROR panicked at 'TODO: write actual tests', testsuite/tests/test.rs:16:9
└─ panic_probe::print_defmt::print @ (..omitted..)
stack backtrace:
0: HardFaultTrampoline
<exception entry>
1: __udf
2: cortex_m::asm::udf
at (..omitted..)
3: rust_begin_unwind
at (..omitted..)
4: core::panicking::panic_fmt
at (..omitted..)
5: core::panicking::panic
at (..omitted..)
6: test::tests::assert_false
at tests/test.rs:16
7: main
at tests/test.rs:7
8: ResetTrampoline
at (..omitted..)
9: Reset
at (..omitted..)
```
NOTE all `#[test]` functions within a file are guaranteed to run sequentially
## Adding `defmt-test` to an existing project
If you want to add `defmt-test` to an existing Cargo project / package, for each *crate* that you want to test you need to do these changes in `Cargo.toml`:
- add `defmt-test` as a `dev-dependency`
- for each crate that you want to test, set `harness` to `false` to disable the default test harness, the `test` crate which depends on `std`. examples below
``` toml
# Cargo.toml
# for the library crate (src/lib.rs)
[lib]
harness = false
# for each crate in the `tests` directory
[[test]]
name = "test-name" # tests/test-name.rs
harness = false
[[test]]
name = "second" # tests/second.rs
harness = false
```
The other thing to be aware is that `cargo test` will compile *all* crates in the package, or workspace.
This may include crates that you don't want to test, like `src/main.rs` or each crate in `src/bin` or `examples`.
To identify which crates are being compiled by `cargo test`, run `cargo test -j1 -v` and look for the `--crate-name` flag passed to each `rustc` invocation.
To test only a subset of the crates in the package / workspace you have two options:
- you can specify each crate when you invoke `cargo test`. for example, `cargo test --lib --test integration` tests two crates: the library crate (`src/lib.rs`) and `tests/integration.rs`
- you can disable tests for the crates that you don't want to test -- example below -- and then you can use `cargo test` to test all crates that were not disabled.
if you have this project structure
``` console
$ tree .
.
├── Cargo.toml
├── src
│ ├── lib.rs
│ └── main.rs
└── tests
└── integration.rs
```
and have `src/lib.rs` set up for tests but don't want to test `src/main.rs` you'll need to disable tests for `src/main.rs`
``` toml
# Cargo.toml
[package]
# ..
name = "app"
[[bin]] # <- add this section
name = "app" # src/main.rs
test = false
```
## Adding state
An `#[init]` function can be written within the `#[tests]` module.
This function will be executed before all unit tests and its return value, the test suite *state*, can be passed to unit tests as an argument.
``` rust
// state shared across unit tests
struct MyState {
flag: bool,
}
#[defmt_test::tests]
mod tests {
#[init]
fn init() -> super::MyState {
// state initial value
super::MyState {
flag: true,
}
}
// This function is called before each test case.
// It accesses the state created in `init`,
// though like with `test`, state access is optional.
#[before_each]
fn before_each(state: &mut super::MyState) {
defmt::println!("State flag before is {}", state.flag);
}
// This function is called after each test
#[after_each]
fn after_each(state: &mut super::MyState) {
defmt::println!("State flag after is {}", state.flag);
}
// this unit test doesn't access the state
#[test]
fn assert_true() {
assert!(true);
}
// but this test does
#[test]
fn assert_flag(state: &mut super::MyState) {
assert!(state.flag)
state.flag = false;
}
}
```
``` console
$ cargo test -p testsuite
0.000000 (1/2) running `assert_true`...
└─ integration::tests::__defmt_test_entry @ tests/integration.rs:37
0.000001 State flag before is true
└─ integration::tests::before_each @ tests/integration.rs:26
0.000002 State flag after is true
└─ integration::tests::after_each @ tests/integration.rs:32
0.000003 (2/2) running `assert_flag`...
└─ integration::tests::__defmt_test_entry @ tests/integration.rs:43
0.000004 State flag before is true
└─ integration::tests::before_each @ tests/integration.rs:26
0.000005 State flag after is false
└─ integration::tests::after_each @ tests/integration.rs:32
0.000006 all tests passed!
└─ integration::tests::__defmt_test_entry @ tests/integration.rs:11
```
## Test Outcome
Test functions may either return `()` and panic on failure, or return any other type that implements the `TestOutcome` trait, such as `Result`.
This allows tests to indicate failure via `Result`, which allows using the `?` operator to propagate errors.
Similar to Rust's built-in `#[should_panic]` attribute, `defmt-test` supports a `#[should_error]` attribute, which inverts the meaning of the returned `TestOutcome`.
`Err` makes the test pass, while `Ok`/`()` make it fail.
## Support
`defmt-test` is part of the [Knurling] project, [Ferrous Systems]' effort at
improving tooling used to develop for embedded systems.
If you think that our work is useful, consider sponsoring it via [GitHub
Sponsors].
## License
Licensed under either of
- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
http://www.apache.org/licenses/LICENSE-2.0)
- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
### Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted
for inclusion in the work by you, as defined in the Apache-2.0 license, shall be
licensed as above, without any additional terms or conditions.
[Knurling]: https://knurling.ferrous-systems.com
[Ferrous Systems]: https://ferrous-systems.com/
[GitHub Sponsors]: https://github.com/sponsors/knurling-rs
