eth2.0-specs/tests/formats/light_client/sync.md

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# Light client sync tests
This series of tests provides reference test vectors for validating that a light client implementing the sync protocol can sync to the latest block header.
## Test case format
### `meta.yaml`
```yaml
genesis_validators_root: Bytes32 -- string, hex encoded, with 0x prefix
trusted_block_root: Bytes32 -- string, hex encoded, with 0x prefix
bootstrap_fork_digest: string -- Encoded `ForkDigest`-context of `bootstrap`
store_fork_digest: string -- Encoded `ForkDigest`-context of `store` object being tested
```
### `bootstrap.ssz_snappy`
An SSZ-snappy encoded `bootstrap` object of type `LightClientBootstrap` to initialize a local `store` object of type `LightClientStore` with `store_fork_digest` using `initialize_light_client_store(trusted_block_rooot, bootstrap)`. The SSZ type can be determined from `bootstrap_fork_digest`.
If `store_fork_digest` differs from `bootstrap_fork_digest`, the `bootstrap` object may need to be upgraded before initializing the store.
### `steps.yaml`
The steps to execute in sequence.
#### Checks to run after each step
Each step includes checks to verify the expected impact on the `store` object.
```yaml
finalized_header: {
slot: int, -- Integer value from store.finalized_header.beacon.slot
beacon_root: string, -- Encoded 32-byte value from store.finalized_header.beacon.hash_tree_root()
execution_root: string, -- From Capella onward; get_lc_execution_root(store.finalized_header)
}
optimistic_header: {
slot: int, -- Integer value from store.optimistic_header.beacon.slot
beacon_root: string, -- Encoded 32-byte value from store.optimistic_header.beacon.hash_tree_root()
execution_root: string, -- From Capella onward; get_lc_execution_root(store.optimistic_header)
}
```
#### `force_update` execution step
The function `process_light_client_store_force_update(store, current_slot)`
should be executed with the specified parameters:
```yaml
{
current_slot: int -- integer, decimal
checks: {<store_attibute>: value} -- the assertions.
}
```
After this step, the `store` object may have been updated.
#### `process_update` execution step
The function `process_light_client_update(store, update, current_slot, genesis_validators_root)` should be executed with the specified parameters:
```yaml
{
update_fork_digest: string -- Encoded `ForkDigest`-context of `update`
update: string -- name of the `*.ssz_snappy` file to load
as a `LightClientUpdate` object
current_slot: int -- integer, decimal
checks: {<store_attibute>: value} -- the assertions.
}
```
If `store_fork_digest` differs from `update_fork_digest`, the `update` object may need to be upgraded before processing the update.
After this step, the `store` object may have been updated.
#### `upgrade_store`
The `store` should be upgraded to reflect the new `store_fork_digest`:
```yaml
{
store_fork_digest: string -- Encoded `ForkDigest`-context of `store`
checks: {<store_attibute>: value} -- the assertions.
}
```
After this step, the `store` object may have been updated.
## Condition
A test-runner should initialize a local `LightClientStore` using the provided `bootstrap` object. It should then proceed to execute all the test steps in sequence. After each step, it should verify that the resulting `store` verifies against the provided `checks`.