Testing in Android

Building on Testing, we will now look at how unit tests work in AOSP. Use the rust_test module for your unit tests:


rust_library {
    name: "libleftpad",
    crate_name: "leftpad",
    srcs: ["src/lib.rs"],

rust_test {
    name: "libleftpad_test",
    crate_name: "leftpad_test",
    srcs: ["src/lib.rs"],
    host_supported: true,
    test_suites: ["general-tests"],


fn main() {
//! Left-padding library.

/// Left-pad `s` to `width`.
pub fn leftpad(s: &str, width: usize) -> String {

mod tests {
    use super::*;

    fn short_string() {
        assert_eq!(leftpad("foo", 5), "  foo");

    fn long_string() {
        assert_eq!(leftpad("foobar", 6), "foobar");

You can now run the test with

atest --host libleftpad_test

The output looks like this:

INFO: Elapsed time: 2.666s, Critical Path: 2.40s
INFO: 3 processes: 2 internal, 1 linux-sandbox.
INFO: Build completed successfully, 3 total actions
//comprehensive-rust-android/testing:libleftpad_test_host            PASSED in 2.3s
    PASSED  libleftpad_test.tests::long_string (0.0s)
    PASSED  libleftpad_test.tests::short_string (0.0s)
Test cases: finished with 2 passing and 0 failing out of 2 test cases

Notice how you only mention the root of the library crate. Tests are found recursively in nested modules.