testing.cases()

A Hypothesis strategy of input tables that meet a node’s preconditions.

Usage

Source

testing.cases(
    node,
    *,
    max_rows=5,
)

Each example maps the name of each table the node reads (as in assert_contract’s data) to an Arrow table of at most max_rows rows. Values are drawn from small ranges, the boundaries of the constants in the node’s plans (sverify.counterexample) and NULL for nullable columns; then the rows that violate a precondition (evaluated by Lean, Rel.eval) are dropped, repeated keys keep their first row, and a foreign key that matches nothing takes a value of the referenced column (or its row goes). So every example meets the preconditions, and the node’s guarantees hold on its output.

Needs Hypothesis (pip install 'sverify[testing]'). Integers, doubles, strings, booleans, dates and timestamps without a time zone are supported.

Parameters

node: Node

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

max_rows: int = 5

The most rows per table. Default: 5.

Returns

SearchStrategy[dict[str, pa.Table]]

A strategy of {table name: pyarrow.Table}.

Raises

TypeError

A column has a type cases cannot generate.

ImportError

Hypothesis is not installed.

Examples

With doubled and orders from assert_contract’s example:

from hypothesis import given, settings
from sverify.testing import cases

node = orders.pipe(doubled)

@settings(max_examples=10, deadline=None)
@given(cases(node))
def test_doubled(data):
    out = assert_contract(node, data=data)
    assert out.num_rows == data["orders"].num_rows

test_doubled()