Python Expect Library

A minimal assertion library inspired by JavaScript's expect (e.g., Chai, Jest) for expressive, readable tests in Python.

Features

• Assert dictionary includes key, value, or subset
• Assert list includes value
• Negation with to_not
• Decorator for asserting raised exceptions with expected messages
• mimic JS expect lib: Expect expect(value) Modifiers .not .resolves .rejects Matchers .toBe(value) .toHaveBeenCalled() .toHaveBeenCalledTimes(number) .toHaveBeenCalledWith(arg1, arg2, ...) .toHaveBeenLastCalledWith(arg1, arg2, ...) .toHaveBeenNthCalledWith(nthCall, arg1, arg2, ....) .toHaveReturned() .toHaveReturnedTimes(number) .toHaveReturnedWith(value) .toHaveLastReturnedWith(value) .toHaveNthReturnedWith(nthCall, value) .toHaveLength(number) .toHaveProperty(keyPath, value?) .toBeCloseTo(number, numDigits?) .toBeDefined() .toBeFalsy() .toBeGreaterThan(number | bigint) .toBeGreaterThanOrEqual(number | bigint) .toBeLessThan(number | bigint) .toBeLessThanOrEqual(number | bigint) .toBeInstanceOf(Class) .toBeNull() .toBeTruthy() .toBeUndefined() .toBeNaN() .toContain(item) .toContainEqual(item) .toEqual(value) .toMatch(regexp | string) .toMatchObject(object) .toMatchSnapshot(propertyMatchers?, hint?) .toMatchInlineSnapshot(propertyMatchers?, inlineSnapshot) .toStrictEqual(value) .toThrow(error?) .toThrowErrorMatchingSnapshot(hint?) .toThrowErrorMatchingInlineSnapshot(inlineSnapshot) Asymmetric Matchers expect.anything() expect.any(constructor) expect.arrayContaining(array) expect.not.arrayContaining(array) expect.closeTo(number, numDigits?) expect.objectContaining(object) expect.not.objectContaining(object) expect.stringContaining(string) expect.not.stringContaining(string) expect.stringMatching(string | regexp) expect.not.stringMatching(string | regexp) Assertion Count expect.assertions(number) expect.hasAssertions() Extend Utilities expect.addEqualityTesters(testers) expect.addSnapshotSerializer(serializer) expect.extend(matchers)

Installation

No installation required. Just copy expect_test.py into your project.

Usage Examples

from expect_test import expect

# Dictionary includes subset
expect({'a': 1, 'b': 2}).to.include({'a': 1})

# Dictionary includes key
expect({'a': 1, 'b': 2}).to.include.key('a')

# Dictionary includes value
expect({'a': 1, 'b': 2}).to.include.value(2)

# List includes value
expect(['a', 'b']).to.include('a')

# Negation
expect({'a': 1, 'b': 2}).to_not.include({'c': 3})
expect({'a': 1, 'b': 2}).to_not.include.key('c')
expect({'a': 1, 'b': 2}).to_not.include.value(3)
expect(['a', 'b']).to_not.include('c')

# Deep dictionary inclusion
expect({'dict_a': {'a': 1, 'b': 2}, 'dict_b': {}}).to.include({'dict_a': {'a': 1, 'b': 2}})

# Asserting exceptions (with pytest)
@assert_raises("assert 'c' in dict_keys(['a', 'b'])")
def test_include_key_is_missing():
    expect({'a': 1, 'b': 2}).to.include.key('c')

Requirements

• Python 3.6+
• pytest (for running tests and using assert_raises)

License

MIT