General test format

This document defines the YAML format and structure used for Eth2 testing.

Table of contents

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Ethereum 2.0 uses YAML as the format for all cross client tests. This document describes at a high level the general format to which all test files should conform.

Test-case formats

The particular formats of specific types of tests (test suites) are defined in separate documents.

Test formats:


  • generator: a program that outputs one or more test-cases, each organized into a config > runner > handler > suite hierarchy.
  • config: tests are grouped by configuration used for spec presets. In addition to the standard configurations, general may be used as a catch-all for tests not restricted to one configuration. (E.g. BLS).
  • type: the specialization of one single generator. E.g. epoch processing.
  • runner: where a generator is a "producer", this is the "consumer".
    • A runner focuses on only one type, and each type has only one runner.
  • handler: a runner may be too limited sometimes, you may have a set of tests with a specific focus that requires a different format. To facilitate this, you specify a handler: the runner can deal with the format by using the specified handler.
  • suite: a directory containing test cases that are coherent. Each suite under the same handler shares the same format. This is an organizational/cosmetic hierarchy layer.
  • case: a test case, a directory in a suite. A case can be anything in general, but its format should be well-defined in the documentation corresponding to the type (and handler).
  • case part: a test case consists of different files, possibly in different formats, to facilitate the specific test case format better. Optionally, a meta.yaml is included to declare meta-data for the test, e.g. BLS requirements.

Test format philosophy

Config design

The configuration constant types are:

  • Never changing: genesis data.
  • Changing, but reliant on old value: e.g. an epoch time may change, but if you want to do the conversion (genesis data, timestamp) -> epoch number, you end up needing both constants.
  • Changing, but kept around during fork transition: finalization may take a while, e.g. an executable has to deal with new deposits and old deposits at the same time. Another example may be economic constants.
  • Additional, backwards compatible: new constants are introduced for later phases.
  • Changing: there is a very small chance some constant may really be replaced. In this off-chance, it is likely better to include it as an additional variable, and some clients may simply stop supporting the old one if they do not want to sync from genesis. The change of functionality goes through a phase of deprecation of the old constant, and eventually only the new constant is kept around in the config (when old state is not supported anymore).

Based on these types of changes, we model the config as a list of key value pairs, that only grows with every fork (they may change in development versions of forks, however; git manages this). With this approach, configurations are backwards compatible (older clients ignore unknown variables) and easy to maintain.

Test completeness

Tests should be independent of any sync-data. If one wants to run a test, the input data should be available from the YAML. The aim is to provide clients with a well-defined scope of work to run a particular set of test-suites.

  • Clients that are complete are expected to contribute to testing, seeking for better resources to get conformance with the spec, and other clients.
  • Clients that are not complete in functionality can choose to ignore suites that use certain test-runners, or specific handlers of these test-runners.
  • Clients that are on older versions can test their work based on older releases of the generated tests, and catch up with newer releases when possible.

Test structure

File path structure:
tests/<config name>/<fork or phase name>/<test runner name>/<test handler name>/<test suite name>/<test case>/<output part>

<config name>/

Configs are upper level. Some clients want to run minimal first, and useful for sanity checks during development too. As a top level dir, it is not duplicated, and the used config can be copied right into this directory as reference.

<fork or phase name>/

This would be: "phase0", "altair", etc. Each introduces new tests, and modifies any tests that change: some tests of earlier forks repeat with updated state data.

<test runner name>/

The well known bls/shuffling/ssz_static/operations/epoch_processing/etc. Handlers can change the format, but there is a general target to test.

<test handler name>/

Specialization within category. All suites in here will have the same test case format. Using a handler in a runner is optional. A core (or other generic) handler may be used if the runner does not have different formats.

<test suite name>/

Suites are split up. Suite size (i.e. the amount of tests) does not change the maximum memory requirement, as test cases can be loaded one by one. This also makes filtered sets of tests fast and easy to load.

<test case>/

Cases are split up too. This enables diffing of parts of the test case, tracking changes per part, while still using LFS. Also enables different formats for some parts.

<output part>

These files allow for custom formats for some parts of the test. E.g. something encoded in SSZ. Or to avoid large files, the SSZ can be compressed with Snappy. E.g. pre.ssz_snappy, deposit.ssz_snappy, post.ssz_snappy.

Diffing a pre.ssz_snappy and post.ssz_snappy provides all the information for testing, when decompressed and decoded. Then the difference between pre and post can be compared to anything that changes the pre state, e.g. deposit.ssz_snappy

Note that by default, the SSZ data is in the given test case's <fork or phase name> version, e.g., if it's altair test case, use altair.BeaconState container to deserialize the given state.

YAML is generally used for test metadata, and for tests that do not use SSZ: e.g. shuffling and BLS tests. In this case, there is no point in adding special SSZ types. And the size and efficiency of YAML is acceptable.

Common output formats

Between all types of tests, a few formats are common:

  • .yaml: A YAML file containing structured data to describe settings or test contents.
  • .ssz: A file containing raw SSZ-encoded data. Previously widely used in tests, but replaced with compressed variant.
  • .ssz_snappy: Like .ssz, but compressed with Snappy block compression. Snappy block compression is already applied to SSZ in Eth2 gossip, available in client implementations, and thus chosen as compression method.

Special output parts


If present (it is optional), the test is enhanced with extra data to describe usage. Specialized data is described in the documentation of the specific test format.

Common data is documented here:

Some test-case formats share some common key-value pair patterns, and these are documented here:

bls_setting: int     -- optional, can have 3 different values:
                            0: (default, applies if key-value pair is absent). Free to choose either BLS ON or OFF.
                                 Tests are generated with valid BLS data in this case,
                                 but there is no change of outcome when running the test if BLS is ON or OFF.
                            1: known as "BLS required" - if the test validity is strictly dependent on BLS being ON
                            2: known as "BLS ignored"  - if the test validity is strictly dependent on BLS being OFF
reveal_deadlines_setting:   -- optional, can have 2 different values:
                            0: default, `process_reveal_deadlines` is ON.
                            1: `process_reveal_deadlines` is OFF.

The runtime-configurables may be different for specific tests. When present, this replaces the default runtime-config that comes with the otherwise compile-time preset settings.

The format matches that of the mainnet_config.yaml and minimal_config.yaml, see the /configs documentation. Config values that are introduced at a later fork may be omitted from tests of previous forks.

Config sourcing

The constants configurations are located in:

<specs repo root>/configs/<config name>.yaml

And copied by CI for testing purposes to:

<tests repo root>/tests/<config name>/<config name>.yaml

The first <config name> is a directory, which contains exactly all tests that make use of the given config.

Note for implementers

The basic pattern for test-suite loading and running is:

  1. For a specific config, load it first (and only need to do so once), then continue with the tests defined in the config folder.
  2. Select a fork. Repeat for each fork if running tests for multiple forks.
  3. Select the category and specialization of interest (e.g. operations > deposits). Again, repeat for each if running all.
  4. Select a test suite. Or repeat for each.
  5. Select a test case. Or repeat for each.
  6. Load the parts of the case. And meta.yaml if present.
  7. Run the test, as defined by the test format.

Step 1 may be a step with compile time selection of a configuration, if desired for optimization. The base requirement is just to use the same set of constants, independent of the loading process.