## testing.assert_engines_agree()


Assert that every engine gives the same rows for a node on `data`.


Usage

``` python
testing.assert_engines_agree(
    node,
    data,
    *,
    engines=None,
)
```


The rows are compared as bags (doubles to 12 significant digits). The data must meet the node's preconditions: outside them the engines may rightly disagree. Each output is also checked against the node's postconditions.


## Parameters


`node: Node`  
A node: a source or node piped into contracted transforms.

`data: Mapping[str, Rows]`  
The rows of each table the node reads, by name (see [assert_contract](testing.assert_contract.md#sverify.testing.assert_contract)).

`engines: Sequence[str] | None = None`  
The engines to compare. Default: [installed_engines()](testing.installed_engines.md#sverify.testing.installed_engines).


## Returns


`pa.Table`  
The first engine's output.


## Raises


`AssertionError`  
The data violates a precondition, an engine fails or violates a postcondition, or two engines give different rows (the message lists the rows that differ from the first engine's).

`ValueError`  
Fewer than two engines, or `data` does not match the tables the node reads.


## Examples

With `doubled` and `orders` from [assert_contract](testing.assert_contract.md#sverify.testing.assert_contract)'s example:

``` python
from sverify.testing import assert_engines_agree

assert_engines_agree(orders.pipe(doubled), {"orders": [(1, 30), (2, 7)]})
```