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

Testing for exceptions

Another requirement is that the price should not be negative. We would want to raise a ValueError if the price is negative. How would we check for this expectation in a test? Here is one way to do that:

    def test_negative_price_should_throw_ValueError(self):
        goog = Stock("GOOG")
            goog.update(datetime(2014, 2, 13), -1)
        except ValueError:
            return"ValueError was not raised")

In the preceding code, we call the update method with a negative price. This call is wrapped with a try...except block to catch ValueError. If the exception is raised correctly, then control goes into the except block where we return from the test. Since the test method returned successfully, it is marked as passing. If the exception is not raised, then the fail method gets called. This is another method provided by unittest.TestCase and raises a test failure exception when it is called. We can pass in a message to provide some...