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

Refactoring the design

In the previous section, we talked about the new requirement of having to check if a stock has an increasing trend.

Let us start by writing a test first:

class StockTrendTest(unittest.TestCase):
    def setUp(self): = Stock("GOOG")
    def test_increasing_trend_is_true_if_price_increase_for_3_updates(self):
        timestamps = [datetime(2014, 2, 11), datetime(2014, 2, 12), datetime(2014, 2, 13)]
        prices = [8, 10, 12]
        for timestamp, price in zip(timestamps, prices):
  , price)

The test takes three timestamps and prices and performs an update for each one. Since all three prices are increasing, the is_increasing_trend method should return True.

To make this test pass, we need to first add support for storing price history.

In the initializer, let us replace the price attribute with a price_history list. This list will store the history of price updates...