assertive

Fluent Assertions

A DSL like assertion library that enables concise high quality assertions in your tests

Assertions

Assertions follow a simple pattern

assert_that(subject).matches(comparison) # object or criteria
assert_that(subject).does_not_match(comparison) # object or criteria

# Same as above
assert_that(subject) == comparison # object or criteria
assert_that(subject) != comparison # object or criteria

Using matchers without criteria, just use classic asserts

assert 2 == is_greater_than(1)

Critera Objects

Critera helps define complex assertions in a concise manner

Some examples of criteria

assert_that(5).matches(is_greater_than(4))
assert_that(5).matches(is_greater_than_or_equal(5))
assert_that(5).matches(is_odd())

Logical criteria operations

assert_that(5).matches(is_odd() & is_greater_than(4)) # And
assert_that(5).matches(is_odd() | is_greater_than(10)) # Or
assert_that(5).matches(~is_even()) # Inverted

Matching

Basic

is_equal_to

assert_that(5).matches(5)
assert_that(5).matches(is_equal_to(5))

assert_that("hello").matches("hello")
assert_that("hello").matches(is_equal_to("hello"))

is_greater_than

assert_that(5).matches(is_greater_than(3))
assert_that(5) == is_greater_than(3)

is_greater_than_or_equal

assert_that(5).matches(is_greater_than_or_equal(5))

is_less_than

assert_that(5).matches(is_less_than(10))

is_less_than_or_equal

assert_that(5).matches(is_less_than_or_equal(10))
assert_that(5).matches(is_less_than_or_equal(5))

is_between

assert_that(5).matches(is_between(5, 10)) # passes
assert_that(5).matches(is_between(5, 10).exclusive) # fails
assert_that(5).matches(is_between(5, 10).inclusive) # passes

is_same_instance_as

x = "hello"
y = x

assert_that(x).matches(is_same_instance_as(y)) # passes

as_string_matches

When the subject called with the str the subject matches the criteria

assert_that(5).matches(as_string_matches("5")) # passes
assert_that(12345).matches(as_string_matches(ends_with("45"))) # passes

Exceptions

Exceptions can be tested in two different ways.

1. As a callable

assert_that(lambda: my_exception_raising_method(123)).matches(raises_exception(Exception))

1. As a context manager

with raises_exception(Exception):
    my_exception_raising_method(123)