assertpy2

Fluent, fully type-aware assertions for Python.

assertpy2 is a modern fork of assertpy: readable assert_that(...) chains, composable matchers, structural matching, soft and async assertions, and a pytest plugin that renders rich structural diffs on failure.

Why assertpy2

• Typed overloads. assert_that("hello"). offers only string methods, assert_that(42). only numeric ones, and a type checker rejects assert_that("foo").is_positive() before the test runs. The core advantage over assertpy and most alternatives - see how it works.
• Composable matchers. match.greater_than(5), match.is_uuid(), combined with &, |, ~.
• Structural matching. Declarative validation of dicts and API responses, with the exact path to each mismatch on failure.
• Soft and async assertions. Collect multiple failures; poll for eventual consistency with eventually().
• Structured failures. AssertionFailure exposes .actual, .expected, and .diff; the pytest plugin renders recursive diffs for lists, dicts, dataclasses, namedtuples, and Pydantic models.

Install

pip install assertpy2

Optional extras: assertpy2[json] (JSONPath / JSON Schema), assertpy2[allure], assertpy2[behave].

Quick example

from assertpy2 import assert_that, match

assert_that("foobar").is_length(6).starts_with("foo").ends_with("bar")
assert_that([1, 2, 3]).contains(1).is_subset_of([1, 2, 3, 4])
assert_that({"id": 1, "name": "Alice"}).matches_structure(
    {"id": match.is_instance_of(int), "name": match.is_non_empty_string()}
)

When a check fails, the pytest plugin points at the exact field instead of dumping both structures:

assert_that(response).matches_structure({
    "user": match.structure({
        "name": match.is_non_empty_string(),
        "role": match.is_in("admin", "user"),
        "age": match.between(18, 120),
    }),
})

See Getting Started to dive in, or browse Type Assertions, Matchers, and the rest of the navigation for the full set of assertions and integrations.