User guide for fx test

This page provides best practices, examples, and reference materials for using the fx test command for running tests in a Fuchsia source checkout setup (fuchsia.git).

Basic usage

To get started, simply run fx test:

fx test

This will do several things:

  1. Identify tests included in your current build.
  2. Select a subset of included tests based on selection criteria.
  3. Rebuild and republish those tests.
  4. Check that an appropriate Fuchsia device exists to run tests on.
  5. In parallel, start running tests on that device and provide status output.
  6. Write a log file describing the operations that occurred.

If you did not include any tests in your build, fx test will exit. Try fx set core.x64--with //src/diagnostics:tests on your fx set command line to include some tests as an example.

For more details on the current status of fx test, see this README page.

Basic concepts

fx test is a Test Executor, which means it ingests a list of available tests and is responsible for scheduling and observing their execution. The source of this data is tests.json.

Each test listed in tests.json is a Test Suite which may each contain any number of Test Cases. That is, a Test Suite is a single binary or Fuchsia Component, and it contains Test Cases which are defined in a way specific to each test framework (e.g. C++ TEST, Rust #[test], Python unittest.TestCase). Enumerating and executing on-device Test Cases is the responsibility of the Test Runner Framework.

Basic test selection

fx test supports selecting individual Test Suites using command line options. This allows you to include a large number of tests in your build and then only execute a subset of those tests.

Any non-flag argument to fx test is a selection that is fuzzy-matched against each test in the input:

fx test archivist --dry

By default, the following fields are searched:

Field Description
name The full name of the test. This is component URL for on-device tests and test binary path for host tests.
label The build label for the test. For example, //src/examples:my_test.
component name The name of the component manifest (excluding .cm) for on-device tests only.
package name The name of the Fuchsia package for on-device tests only.

You can select all tests below a directory in the source tree by listing the prefix:

fx test //src/diagnostics/tests --dry

By default all of the above fields are matched, but you can select specific fields using --package or --component:

fx test --package archivist_unittests --dry

By default, multiple selections on the command line implement an inclusive-OR operation. Test selection supports composite AND operations as follows:

fx test --package archivist --and unittests --dry

This command selects all tests where the package matches archivist and any field matches unittests.

If you know the exact name of the test you want to execute, you may use the --exact flag to select only that test:

fx test --exact fuchsia-pkg:// --dry

If no tests match your selection, fx test will try to heuristically match tests in your source checkout and suggest fx set arguments to include them:

$ fx test driver-tests --dry
For `driver-tests`, did you mean any of the following?

driver_tools_tests (91.67% similar)
    --with //src/devices/bin/driver_tools:driver_tools_tests
driver-runner-tests (90.96% similar)
    --with //src/devices/bin/driver_manager:driver-runner-tests
driver-inspect-test (90.96% similar)
    --with //src/devices/tests/driver-inspect-test:driver-inspect-test

You can then add the necessary packages to your build.

Basic test output

fx test stores its output in log files for later analysis. You can view a summary of this log file in text form using the -pr/--previous argument. For example, to see test logs from the previous run:

$ fx test -pr log

4 tests were run

[START first_test]
[END first_test]

For a full list of options for processing previous log files, run fx test -pr help.

By default this command processes the most recent log stored in your Fuchsia output directory, but you may pass --logpath to choose a specific log.

This command is resilient to corrupt or incomplete log files, so it should still work even if you terminate the fx test command running the tests.

Basic test debugging

fx test integrates with zxdb to provide a simple and easy way to debug your test failures, without needing to recompile anything. Pass --break-on-failure to your fx test invocation to automatically have test failures break into the debugger:

$ fx test --break-on-failure
⚠️  zxdb caught test failure in, type `frame` to get started.
   14 LLVM_LIBC_FUNCTION(void, abort, ()) {
   15   for (;;) {
   17     _zx_process_exit(ZX_TASK_RETCODE_EXCEPTION_KILL);
   18   }
 Invalid opcode exception
 Process 1 (koid=107752) thread 1 (koid=107754)
 Faulting instruction: 0x4159210ab797

🛑 process 1 __llvm_libc::__abort_impl__() •
[zxdb] // Now you can debug why the test failed!

You can also use the --breakpoint=<location> option to set a breakpoint at a specific location anywhere in your code. <location> takes standard zxdb breakpoint syntax, typically a file and line number or a function name:

  • sets a breakpoint on line 123 of
  • --breakpoint=some_function sets a breakpoint on some_function.

Note that this option will cause your tests to run significantly slower, since zxdb will need to load all of the symbols for your test to be able to install the breakpoint. It is highly recommended to only use this option in addition to --test-filter.

When you're finished debugging the test failure, you can type quit, ctrl+d, or detach * to resume running your tests. Note, if there were multiple test case failures, this will not pause to let you debug those tests as well. See debugging tests for details about how to debug multiple test failures that occur in parallel.

Configuration options

fx test is highly configurable, and a full list of options is available at fx test --help.

This section describes how configuration options are specified and what they mean. Configuration options are categorized as Utility, Build, Test Selection, Execution, or Output Options. They may be specified on the command line or in a configuration file.

Configuration file

All arguments for fx test are set on the command line, but defaults may be set per-user. If you place a file called .fxtestrc in your HOME directory, the arguments in that file will be the new defaults for future fx test invocations.

For example:

# ~/.fxtestrc
# Lines starting with "#" are comments and ignored.
# The below config roughly matches the behavior of the old Dart-based `fx test`.

# Default parallel to 1.
--parallel 1

# Disable status output.

# Print output for tests taking longer than 2 seconds.
--slow 2

The above file overrides the defaults for --parallel and --status flags, which normally default to 4 and false respectively. The new defaults may still be overridden on the command line when invoking fx test.

Utility options

Utility options change the overall behavior of fx test.

--dry performs a "dry-run." fx test will complete test selection, but will then simply print the list of selected test suites rather than executing any of them.

--list runs fx test in "list mode." Rather than executing tests, this command lists all test cases within each test suite. It outputs the appropriate command line to run each individual case. Note that this does require access to a Fuchsia device or emulator because cases are enumerated by Test Manager on device.

-pr/--prev/--previous COMMAND will process the log file from a previous execution of fx test, and will print information depending on the value of COMMAND. No new tests are executed. This command respects --logpath to specify the log to read from.

The following COMMANDs are implemented:

  • log prints the command line and output for each test recorded in the log file.
  • help prints a summary of available commands.

Build options

fx test builds and updates selected tests by default. This is useful when running fx -i test, which will detect changes to your source directory and re-invoke fx test following each file modification. Test rebuilding works as follows (with overrides listed inline).

  • All selected tests are rebuilt by calling fx build <targets> for each fx test invocation.
    • Use --[no-]build to toggle this behavior.
  • If selected tests are in the "base packages" for your build (specified using fx set --with-base), the updates package will be built and an OTA will be performed.
    • Use --[no-]updateifinbase to toggle this behavior.
    • Warning: OTA will fail when targeting an emulator.

Test selection options

The following options affect which tests are selected by fx test and how selections are applied.

--host and --device select only host or device tests respectively. This is a global setting and they cannot be combined.

--[no-]e2e controls whether to run end-to-end (E2E) tests. E2E tests are not run by default because they have the potential to put the device in an invalid state. --only-e2e implies --e2e, and ensures that only E2E tests are selected.

--package (-p) and --component (-c) select within package or component names respectively. Names preceded by neither select any test field. Multiple selections may be changed by --and (-a). For example:

fx test --package foo -a --component bar //src/other --and --package my-tests

The above command line contains two selection clauses:

  1. Package "foo" AND component "bar" (e.g. fuchsia-pkg://
  2. Package "my-tests" AND //src/other.

Tests matching either of the above clauses are selected.

Test selections are fuzzy-matched using a Damerau-Levenshtein distance of 3 by default (e.g. "my_tset" will match "my-test"). --fuzzy <N> can be used to override this value to N, where 0 means not to do fuzzy matching.

Suggestions are shown by default if no test matches a selection clause. The number of suggestions (default 6) can be overridden using --suggestions-count N, and suggestions can be disabled or enabled using --[no-]show-suggestions.

Execution options

Tests are executed in a specific way that maximizes throughput and stability, but each element of this default may be overridden. Tests are executed as follows (with overrides listed inline):

  • Each selected test is executed in the order they appear within tests.json
    • Use --random to randomize this execution order.
  • All selected tests are run, starting at the beginning of the ordered list above.
    • Use --offset N to skip N tests at the beginning of the list. Default is 0.
    • Use --limit N to run at most N tests from the offset. Default is no limit.
  • At most 4 tests may run in parallel, such that at most one of those tests is "non-hermetic" (as determined by test-list.json).
    • Use --parallel N to change this default. --parallel 1 means to execute each test serially.
  • Tests run until they terminate themselves.
    • Use --timeout N to wait at most N seconds per test.
  • Each test runs one time.
    • Use --count N to run each test N times.
  • All test cases are run from each test.
    • Use --test-filter to run only specifically named test cases.
  • Failed tests are recorded and execution continues with the next selected test.
    • Use --fail (-f) to terminate all tests following the first failure.
  • Tests that specify a maximum log level in tests.json will fail if logs at a higher severity are seen.
    • Use --[no-]restrict-logs to toggle this behavior.
  • Tests components themselves choose the minimum log severity to emit.
    • Use --min-severity-logs to override this minimum for all test components.
  • Test components are run using the Merkle root hash from build artifacts, which ensures that the latest version built was successfully pushed to the target and is being run.
    • Use --[no-]use-package-hash to toggle this behavior.
  • Test cases that are disabled are not run.
    • Use --also-run-disabled-tests to run disabled test cases anyway.
  • Test output logs contain only the last segment of the component moniker, so they are easier to visually inspect.
    • Use --[no-]show-full-moniker-in-logs to toggle this behavior.
  • Failing tests terminate following failure without waiting

    • Use --break-on-failure to catch failing tests with zxdb.
    • Use --breakpoint=<location> to install breakpoints at specific [locations][#basic-test-debugging].

    Note that using the --breakpoint option will significantly slow down your tests. It is highly recommended to only use this option in conjunction with --test-filter. --break-on-failure may be used with many tests with minimal impact to performance.

  • Command line arguments to the test are completely controlled by test runners

    • Append -- to your arguments to pass remaining arguments verbatim to the test. For example: fx test foo -- --argument_for_test will pass --argument_for_test to the test itself.
  • Host tests will inherit a limited set of environment variables from the user's environment automatically

    • Use --env (-e) to add new KEY=VALUE environment variables to tests. This flag may be specified multiple times.

Output options

fx test is intended for developer use cases and includes a simple terminal UI that displays the status of tests as they are executing. The default output behavior is as follows (with overrides listed inline):

  • A status display is shown at the bottom of the terminal, and it is automatically updated to show what operations are currently executing.
    • Use --[no-]status to toggle status display.
    • Use --status-lines N to change the number of status output lines.
    • Use --status-delay N to change the refresh rate (default is 0.033 or approximately 30hz). If your terminal is slow you may want to change this to 0.5 or 1.
  • Output is styled with ANSI terminal colors.
    • Use --[no-]style to toggle this behavior.
    • Use --simple as shorthand for --no-style --no-status.
  • Test outputs are only shown for tests that fail.
    • Use --output (-o) to show all test output (combine with --parallel 1 to prevent interleaving).
    • Use --no-output to hide output explicitly, such as to override --output set in config.
    • Use --slow N (-s N) to show output only for test suites that take longer than N seconds to execute.
  • Logs are written to a timestamped .json.gz file under the build directory specified by fx status.
    • Use --[no-]log to toggle logging entirely.
    • Use --logpath to change the output path of the log.
  • Test artifacts are not streamed off of the device.
    • Use --artifact-output-directory (--outdir) to specify a directory where artifacts may be streamed in the ffx test output format.
  • Debug printing is suppressed.
    • Use --verbose (-v) to print debug information to the console. This data is extremely verbose, and is only useful to debug fx test itself.

Log Format

fx test is designed to support external tooling by representing every user-visible output as an "event" which is logged to a file during execution.

Log files are compressed using gzip. Each line of the decompressed file is a single JSON object representing one event. The event schema is currently defined in this Python file.

When the format is stabilized, it will be possible to build interactive viewers and converters to other formats (such as Build Event Protocol).

Common issues

fx test does not work with emacs

The emacs compilation window does not emulate an xterm-compatible terminal, resulting in an error like below:

in _make_progress_bar raise ValueError("Width must be at least 3")

To solve this problem, run fx test with the --no-status option to disable the status bar.

Escape sequences appear in fx test output

Your terminal may not support ANSI color codes, which fx test fails to detect.

Pass the --no-style option to fx test to disable color output or the --no-status option to disable the updating status bar. Passing the --simple option to fx test is equivalent to --no-style --no-status.

I don't know where my log file is

You can set the location of the log by passing --logpath to fx test, though this is recommended only for non-interactive use.

By default, your logs are stored in your Fuchsia output directory as timestamped files. Print the path to the previous logs using fx test -pr path.

Printing the log file dumps garbage into my terminal

fx test logs are gzipped by default. Use the following command to pretty print the most recent log to your terminal:

cat `fx test -pr path` | gunzip | jq -C | less -R

This command does the following:

  • Find the most recent log path (fx test -pr path).
  • Pipe the log to gunzip to decompress the log.
  • Pipe the decompressed log to jq to pretty-print it with color output (-C).
  • Pipe the color output to less configured to display color (-R).

For convenience, you can add an alias for this command in your .bashrc file:

alias testlog='cat `fx test -pr path` | gunzip | jq -C | less -R'

Opting out of the new fx test command

The new fx test command is currently set to be the default.

To opt out of this setting, set the following environment variable:

export FUCHSIA_DISABLED_legacy_fxtest=0