Asserto:

Asserto is a clean, fluent and powerful assertion library for python. We recommend using pytest as a test runner but asserto will work well with any test runner.

Asserto was developed using pytest as it's test runner and has a pytest-asserto plugin that exposes asserto through a fixture. Asserto will work on any runner or even without one. Note: It is common practice for a test runner to apply assertion rewriting to change the behaviour of the assert keyword under the hood.

The main features of asserto are (and will be):

• Chainable and Fluent API.
• Ability for both Hard and Soft assertions.
• Rich diffs to highlight problems, reduce churn and improve efficiency and debug-ability.
• Dynamic assertions; check any obj attribute or invoke any of its function types.
• Robust set of methods out of the box for common types.
• Extensibility. Bolt on your own assertions at runtime.
• Human error detection, elaborate warnings when something is amiss.
• Much more to come.

Feature Set:

Fluent API:

Asserto exposes a fully fluent API for chaining assertions against a value.

from asserto import asserto


def test_multiple_assert_fluency() -> None:
    asserto("Hello").has_length(5).match(r"\w{5}$").ends_with("lo").starts_with("Hel")

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Soft Assertions:

Asserto Has soft capabilities; allowing multiple assertions to be performed before failing with a summary of the failures.

from asserto import asserto

def test_baz() -> None:
    with asserto("Baz") as context:
        # asserto when used in a python context is run in 'soft' mode;
        # upon exiting the context; congregated errors are subsequently raised (if any)
        context.starts_with("B").ends_with("z").is_equal_to("Baz").has_length(2)  # Ends in a failure.

Will result in the following:

    def test_foo(asserto) -> None:
>       with asserto("Bar") as context:
E       AssertionError: 1 Soft Assertion Failures
E       [AssertionError("Length of: 'Bar' was not equal to: 2")]

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Exception Handling:

Asserto has the ability to assert exceptions are raised on callables using a simple API.

from asserto import asserto
import typing


def simple_callable(x: int) -> typing.NoReturn:
    raise ValueError(x)


def test_exc_handling():
    asserto(simple_callable).should_raise(ValueError).when_called_with(25)

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Dynamic Lookups:

Asserto has the ability to dynamically lookup attributes on any object type. This is handled using the attr_is(expected) syntax.

from asserto import asserto


class Foo:

    def __init__(self, x) -> None:
        self.x = x

    def double_x(self) -> int:
        return self.x * 2


def test_foo_dynamically() -> None:
     # dynamically looking up `x` (attr) or `double_x` bound method & invoking it!
    asserto(Foo(10)).x_is(10).double_x_is(20)

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Dynamic assert registration

Asserto allows users to easily bolt on their assertion functions.

from asserto import asserto
from asserto import register_assert


@register_assert  # Option 1.
def custom_assert(self):
    if self.actual != 5:
        self.check_should_raise(f"{self.actual} did not equal five!")


register_assert(custom_assert)  # Option 2


def test_user_defined_callables() -> None:
    asserto(6).custom_assert()

yields the following:

E       AssertionError: 6 did not equal five!

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