Testing utility library

This library implements helpers for writing e2e tests for ffx subtools.

It includes:

  • A testing fixture to reduce setup boilerplate
  • A hermetic execution environment for ffx (via ffx_isolate)
  • Low-level emulator spawning utilities (for flash and OTA testing)

And is planned to include:

  • Matchers for ffx command output (b/293217132)
  • ffx emu integration by merging with ffx_e2e_emu (b/295230484)


Subtool e2e tests typically live in src/developer/ffx/tests. This is akin to ffx self-test but using rustc_test to execute tests instead of a subtool.

In BUILD.gn:


if (is_host) {
  rustc_test("ffx_<something>_test") {
    testonly = true
    edition = "2021"
    source_root = "src/tests.rs"

    sources = [ "src/tests.rs" ]

    deps = [

    # If using ffx_testing::Emu: Only one emulator can be spawned at a time.
    # These lower level emulators use TAP networking, which is required for IPv6
    # support.
    # args = [ "--test-threads=1" ]

In src/tests.rs:

use ffx_testing::{base_fixture, TestContext};
use fixture::fixture;

// base_fixture sets up the test environment this test
async fn my_test(ctx: TestContext) {
  let _daemon = ctx.isolate().start_daemon().await.unwrap();

  let output = ctx.isolate().ffx(&["daemon", "echo"]).await.expect("daemon echo");

Low Level Emulators

A low-level emulator can be brought up with Emu::start. It can be controlled via serial and talked to by ffx. For a test that uses the emulator, see ffx_target_test.

/!\ This emulator is brought up with an empty disk /!\

This is by design. To e2e test with a fuchsia image use the ffx_e2e_emu library under //src/developer/ffx/lib/e2e_emu.

use ffx_testing::Emu;

let emu = Emu::start(&ctx);

// NOTE: If using serial, make sure to drain or close the serial stream when no longer in use.
// Failure to do so will result in QEMU halting.
  let serial = emu.serial().await;

  // ...

// Dropping or letting the emu go out of scope cleans up the emulator.