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Firecracker Integration Tests

The tests herein are meant to uphold the security, quality, and performance contracts of Firecracker.

Running

To run all tests:

tools/devtool test

This will download test microvm images from the default test resource S3 bucket and run all available tests.

To run tests from specific directories and/or files:

tools/devtool test -- <test_dir_or_file_path>...

The testing system is built around pytest. Any parameters passed to tools/devtool test -- are passed to the pytest command. devtool is used to automate fetching of test dependencies (useful for continuous integration) and to sandbox test runs (useful for development environments). If you are not interested in these capabilities, use pytest directly, either from inside the container:

tools/devtool shell -p
pytest [<pytest argument>...]

Or natively on your dev box:

python3 -m pytest [<pytest argument>...]

For help on usage, see tools/devtool help.

Output

  • Output, including testrun results, goes to stdout. Errors go to stderr.

Dependencies

  • A bare-metal Linux host with uname -r >= 4.14.
  • Docker.

Rustacean Integration Tests

The pytest-powered integration tests rely on Firecracker's HTTP API for configuring and communicating with the VMM. Alongside these, the vmm crate also includes several native-Rust integration tests, which exercise its programmatic API without the HTTP integration. Cargo automatically picks up these tests when cargo test is issued. They also count towards code coverage.

To run only the Rust integration tests:

cargo test --test integration_tests

Unlike unit tests, Rust integration tests are each run in a separate process. Cargo also packages them in a new crate. This has several known side effects:

  1. Only the pub functions can be called. This is fine, as it allows the VMM to be consumed as a programmatic user would. If any function is necessary but not pub, please consider carefully whether it conceptually needs to be in the public interface before making it so.

  2. The correct functioning scenario of the vmm implies that it exits with code 0. This is necessary for proper resource cleanup. However, cargo doesn't expect the test process to initiate its own demise, therefore it will not be able to properly collect test output.

    Example:

    cargo test --test integration_tests
running 3 tests
test test_setup_serial_device ... ok

To learn more about Rustacean integration test, see the Rust book.

Adding Python Tests

Tests can be added in any (existing or new) sub-directory of tests/, in files named test_*.py.

Fixtures can be used to quickly build Firecracker microvm integration tests that run on all microvm images in s3://spec.ccfc.min/img/.

For example, the test below makes use of the test_microvm_any fixture and will be run on every microvm image in the bucket, each as a separate test case.

def test_with_any_microvm(test_microvm_any):
    response = test_microvm_any.machine_cfg.put(
        vcpu_count=2
    )
    assert(test_microvm_any.api_session.is_good_response(response.status_code))

    # [...]

    response = test_microvm_any.actions.put(action_type='InstanceStart')
    assert(test_microvm_any.api_session.is_good_response(response.status_code))

If instead of test_microvm_any, a capability-based fixture would be used, e.g., test_microvm_with_net, then the test would instead run on all microvm images with the capability:net tag.

To see what fixtures are available, inspect conftest.py.

Adding Rust Tests

Add a new function annotated with #[test] in integration_tests.rs.

Adding Microvm Images

Simply place the microvm image under s3://spec.ccfc.min/img/. The layout is:

s3://<bucket-url>/img/
    <microvm_test_image_folder_n>/
        kernel/
            <optional_kernel_name.>vmlinux.bin
        fsfiles/
            <rootfs_name>rootfs.ext4
            <optional_initrd_name.>initrd.img
            <other_fsfile_n>
            ...
        <other_resource_n>
        ...
    ...

Then, tag <microvm_test_image_folder_n> with:

TagSet = [{"key": "capability:<cap_name>", "value": ""}, ...]

For example, this can be done from the AWS CLI with:

aws s3api put-object-tagging                    \
    --bucket ${bucket_name}                     \
    --key img/${microvm_test_image_folder_n}    \
    --tagging "TagSet=[{Key=capability:${cap_name},Value=''}]"

Adding Fixtures

By default, pytest makes all fixtures in conftest.py available to all test functions. You can also create conftest.py in sub-directories containing tests, or define fixtures directly in test files. See pytest documentation for details.

Working With Guest Files

There are helper methods for writing to and reading from a guest filesystem. For example, to overwrite the guest init process and later extract a log:

def test_with_any_microvm_and_my_init(test_microvm_any):
    # [...]
    test_microvm_any.slot.fsfiles['mounted_root_fs'].copy_to(my_init, 'sbin/')
    # [...]
    test_microvm_any.slot.fsfiles['mounted_root_fs'].copy_from('logs/', 'log')

copy_to() source paths are relative to the host root and destination paths are relative to the mounted_root_fs root. Vice versa for copy_from().

Copying files to/from a guest file system while the guest is running results in undefined behavior.

Example Manual Testrun

Running on an EC2 .metal instance with an Amazon Linux 2 AMI:

# Get firecracker
yum install -y git
git clone https://github.com/firecracker-microvm/firecracker.git

# Run all tests
cd firecracker
tools/devtool test

Terminology

  • Testrun: A sandboxed run of all (or a selection of) integration tests.
  • Test Session: A pytest testing session. One per testrun. A Testrun will start a Test Session once the sandbox is created.
  • Test: A function named test_ from this tree, that ensures a feature, functional parameter, or quality metric of Firecracker. Should assert or raise an exception if it fails.
  • Fixture: A function that returns an object that makes it very easy to add Tests: E.g., a spawned Firecracker microvm. Fixtures are functions marked with @pytest.fixture from a files named either conftest.py, or from files where tests are found. See pytest documentation on fixtures.
  • Test Case: An element from the cartesian product of a Test and all possible states of its parameters (including its fixtures).

FAQ

Q1: I have a shell script that runs my tests and I don't want to rewrite it. A1: Insofar as it makes sense, you should write it as a python test function. However, you can always call the script from a shim python test function. You can also add it as a microvm image resource in the s3 bucket (and it will be made available under microvm.slot.path) or copy it over to a guest filesystem as part of your test.

Q2: I want to add more tests that I don't want to commit to the Firecracker repository. A2: Before a testrun or test session, just add your test directory under tests/. pytest will discover all tests in this tree.

Q3: I want to have my own test fixtures, and not commit them in the repo. A3: Add a conftest.py file in your test directory, and place your fixtures there. pytest will bring them into scope for all your tests.

Q4: I want to use more/other microvm test images, but I don't want to add them to the common s3 bucket. A4: Add your custom images to the build/img subdirectory in the Firecracker source tree. This directory is bind-mounted in the container and used as a local image cache.

Q5: Is there a way to speed up integration tests execution time? A5: You can speed up tests execution time with any of these:

  1. Run the tests from inside the container and set the environment variable KEEP_TEST_SESSION to a non-empty value.

    Each Testrun begins by building the firecracker and unit tests binaries, and ends by deleting all the built artifacts. If you run the tests from inside the container, you can prevent the binaries from being deleted exporting the KEEP_TEST_SESSION variable. This way, all the following Testrun will be significantly faster as they will not need to rebuild everything. If any Rust source file is changed, the build is done incrementally.

  2. Pass the -k substring option to Pytest to only run a subset of tests by specifying a part of their name.

  3. Only run the tests contained in a file or directory, as specified in the Running section.

Implementation Goals

  • Easily run tests manually on a development/test machine, and in a continuous integration environments.
  • Each test should be independent, and self-contained. Tests will time out, expect a clean environment, and leave a clean environment behind.
  • Always run with the latest dependencies and resources.

Choice of Pytest & Dependencies

Pytest was chosen because:

  • Python makes it easy to work in the clouds.
  • Python has built-in sandbox (virtual environment) support.
  • pytest has great test discovery and allows for simple, function-like tests.
  • pytest has powerful test fixture support.

Test System TODOs

Note: The below TODOs are also mentioned in their respective code files.

Features

  • Modify MicrovmImageS3Fetcher to make the above FAQ possible (the borg pattern is wrong for this).
  • A fixture for interacting with microvms via SSH.
  • Support generating fixtures with more than one capability. This is supported by the MicrovmImageS3Fetcher, but not plumbed through.
  • Use the Firecracker Open API spec to populate Microvm API resource URLs.
  • Manage output better: handle quietness levels, and use pytest reports.
  • Do the testrun in a container for better insulation.
  • Add support for non-Rust style checks.
  • Event-based monitoring of microvm socket file creation to avoid while spins.
  • Self-tests (e.g., Tests that test the testing system, python3 style tests).

Implementation

  • Looking into pytest-ordering to ensure test order.
  • Create an integrated, layered say system across the test runner and pytest (probably based on an environment variable).
  • Per test function dependency installation would make tests easier to write.
  • Type hinting is used sparsely across tests/* python module. The code would be more easily understood with consistent type hints everywhere.

Bug fixes

  • Fix the /install-kcov.sh bug.

Further Reading

Contributing to this testing system requires a dive deep on pytest.