Book Image

Test-Driven Python Development

By : Siddharta Govindaraj
Book Image

Test-Driven Python Development

By: Siddharta Govindaraj

Overview of this book

This book starts with a look at the test-driven development process, and how it is different from the traditional way of writing code. All the concepts are presented in the context of a real application that is developed in a step-by-step manner over the course of the book. While exploring the common types of smelly code, we will go back into our example project and clean up the smells that we find. Additionally, we will use mocking to implement the parts of our example project that depend on other systems. Towards the end of the book, we'll take a look at the most common patterns and anti-patterns associated with test-driven development, including integration of test results into the development process.
Table of Contents (20 chapters)
Test-Driven Python Development
About the Author
About the Reviewers

Exploring assert methods

Now we have just one requirement for update remaining:

  • -Done- It should take a timestamp and price value and set it on the object

  • -Done- The price cannot be negative

  • After multiple updates, the object gives us the latest price

Let us take the remaining requirement. Here is the test:

    def test_stock_price_should_give_the_latest_price(self):
        goog = Stock("GOOG")
        goog.update(datetime(2014, 2, 12), price=10)
        goog.update(datetime(2014, 2, 13), price=8.4)
        self.assertAlmostEqual(8.4, goog.price, delta=0.0001)

What this test does is to simply call update twice, and when we ask for the price, provide us with the newer one. The interesting point about the test is that we use the assertAlmostEqual method here. This method is often used when checking equality with floating point numbers. Why don't we use plain old assertEqual? The reason is that due to the way floating points are stored, the result may not be exactly the number you expect. There...