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#93 in Testing

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Testing framework for the Game Boy Advance.

Example .gif

Getting Started

Using gba_test requires a nightly Rust version.


  • ARM Binutils: At minimum, you'll need the ARM GNU linker (arm-none-eabi-ld) to properly build projects using gba_test. You can obtain it from the ARM website.
  • rust-src - GBA development requires build-std to work. Run rustup component add rust-src to enable it.
  • cargo configuration - Configuration for cargo should be provided in a cargo/config.toml file within your project. An example configuration is as follows:
target = "thumbv4t-none-eabi"

runner = "mgba"
rustflags = ["-Clinker=arm-none-eabi-ld", "-Clink-arg=-Tgba.ld", "-Ztrap-unreachable=no"]

build-std = ["core"]

Adding gba_test to your list of dependencies

In your Cargo.toml manifest, add gba_test to your list of dev-dependencies:

name = "your_project"
version = "0.1.0"
edition = "2021"

gba_test = "0.1.0"

Running the test runner

gba_test provides its own test runner. To run the tests, you'll need to call the runner from your main() function.

The following code can be used to call the test runner when you run cargo test:

#![cfg_attr(test, no_main)]
#![cfg_attr(test, feature(custom_test_frameworks))]
#![cfg_attr(test, test_runner(gba_test::runner))]
#![cfg_attr(test, reexport_test_harness_main = "test_harness")]

pub fn main() {

Calling test_harness() will run all tests defined within your project.

Defining tests

gba_test provides its own custom #[test] attribute for defining tests. It works similar to the default #[test] attribute.

// A very simple function to test.
pub fn add(left: usize, right: usize) -> usize {
    left + right

mod tests {
    use super::add;
    use gba_test::test;

    fn it_works() {
        let result = add(2, 2);
        assert_eq!(result, 4);

Other common testing attributes are also supported, including #[ignore] and #[should_panic].

Running Tests

gba_test can be run on anything that runs .gba files, ranging from original Game Boy Advance hardware to emulators.

Configuring to run on mGBA with cargo test

For development workflows, it is recommended to run tests on an emulator. The example cargo/config.toml provided in the "Prerequisites" section will enable you to run tests on mGBA (assuming mgba is in your PATH) when you run cargo test.

Running on real hardware

To run on real Game Boy Advance hardware, you can flash the generated test binary to a cartridge.

Preparing a .gba file

When running cargo test, a .elf test binary is generated. Emulators like mGBA can run this .elf file, but real hardware requires a .gba file. The location of your test binary is output by cargo test. For example, running cargo test on the gba_test library itself outputs something like:

Running unittests src\lib.rs (target\thumbv4t-none-eabi\debug\deps\gba_test-5b5cf1bdf24b2915)

The path in the parenthesis is the location of the test binary. You can use arm-none-eabi-objcopy (obtained from the ARM website) to create a .gba file from this binary:

arm-none-eabi-objcopy -O binary target\thumbv4t-none-eabi\debug\deps\gba_test-5b5cf1bdf24b2915 test.gba

Next, run gbafix:

cargo install gbafix
gbafix test.gba

Now, test.gba is prepared to run on real Game Boy Advance hardware. See documentation for your flash cart for instructions on flashing the .gba file to the cartridge and running it.

Running using mgba-rom-test

gba_test is configured to be run with the mgba-rom-test binary using SWI call 0x27 with r0 as the output register. An exit value of 0 is considered a successful test run.

To use mgba-rom-test in continuous integration with GitHub Actions, it is recommended to use the github-mgba-rom-test action. See this project's GitHub Actions setup for examples of this workflow.


Some emulators, such as mGBA or no$gba, support logging. gba_test provides optional integration with the log crate to log information about test running. You can enable logging through the log feature:

gba_test = {version = "0.1.0", features = ["log"]}

You can also log within your tests using the log crate:

use gba_test::test;

fn foo() {
    log::info!("important information");

To produce the log output for your emulator, you'll need to use a logger implementation specific for that emulator's logging interface. The following logger implementations are recommended:

Initialize the logger prior to calling the test runner, like so:

#![cfg_attr(test, no_main)]
#![cfg_attr(test, feature(custom_test_frameworks))]
#![cfg_attr(test, test_runner(gba_test::runner))]
#![cfg_attr(test, reexport_test_harness_main = "test_harness")]

pub fn main() {


This project is licensed under either of

at your option.


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 dual licensed as above, without any additional terms or conditions.