Chapter 8. Assure Quality with Testing

Some programmers test only in production. If you are not one of them you're probably familiar with the concept of unit testing. Unit tests are automated tests written by a programmer to test his or her code. These tests could, for example, test a function or part of a function in isolation. Only a small unit of code is tested by each test. The benefits are increased confidence in the quality of the code, reproducible tests, and as a side effect, more clear code.

Python has good support for unit testing. Additionally, NumPy adds the numpy.testing package to that for NumPy code unit testing.

Test driven development (TDD) is one of the most important things that happened to software development. TDD focuses a lot on automated unit testing. The goal is to test automatically as much as possible of the code. The next time the code is changed we can run the tests and catch potential regressions. In other words functionality already present will still work.

This chapter's topics include:

  • Unit testing
  • Asserts
  • Floating point precision

Assert functions

Unit tests usually use functions, which assert something as part of the test. When doing numerical calculations, often we have the fundamental issue of trying to compare floating-point numbers that are almost equal. For integers, comparison is a trivial operation, but for floating-point numbers it is not because of the inexact representation by computers. The numpy.testing package has a number of utility functions that test whether a precondition is true or not, taking into account the problem of floating-point comparisons:

Function

Description

assert_almost_equal

Raises an exception if two numbers are not equal up to a specified precision

assert_approx_equal

Raises an exception if two numbers are not equal up to a certain significance

assert_array_almost_equal

Raises an exception if two arrays are not equal up to a specified precision

assert_array_equal

Raises an exception if two arrays are not equal

assert_array_less

Raises an exception if two arrays do not have the same shape and the elements of the first array are strictly less than the elements of the second array

assert_equal

Raises an exception if two objects are not equal

assert_raises

Fails if a specified exception is not raised by a callable invoked with defined arguments

assert_warns

Fails if a specified warning is not thrown

assert_string_equal

Asserts that two strings are equal

assert_allclose

Raise an assertion if two objects are not equal up to desired tolerance

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