Monday, April 8, 2013

The Power of Data-Driven Testing

This post assumes a focus on integration and end-to-end testing of the less-dependent parts of a product, where the greatest quality risks are found: in the business logic, data or cloud layers. See this post for a discussion of why this is most effective for a product that has important information:

Automated testing usually involves some inline code in a class method. A common pattern is to copy and paste code, or create test libs with some shared operations and call the libs from the test method. The tests correspond to the methods 1:1, so 50 automated tests look like 50 methods on a class with minor hard-coded variations between repeated patterns in code.

For repeated patterns like this, there’s a much better way: data-driven testing.

Data-driven tests use a data source to drive the tests. Within the limits of a pattern of testing as defined by the capabilities of the system reading the data to drive the test, each set of data for the pattern drives an individual test. The set of data for each test could be a row in a relational database table or view, or an XML element of a certain type in an XML document or file.

Why is this better?

For one, agility. The test set can be modified to fit product changes with changes in the test-driving data, at very low risk. It can also be extended as far as you want, within limits described by how the data is read.

Helping the agility comes readability, meaning that it’s easy for anyone to see what is tested and what is not for a given test set. It’s easy to verify that the equivalence classes you want covered are represented for a given set, or the pairwise sets are there, boundaries are checked with positive and negative tests, etc. for a given test set.

To help readability, you can put readable terms into your test-driving data. Containers can have “null” or an integer count or something else. Enumerated types can be a label used in the type, say “Green,” “Red” or “Blue”, or the integer -1 or 4 for negative limit tests.

Best of all, failure of a specific test can be tracked with a bug number or a note, for example, “Fernando is following up on whether this behavior is by-design” or “Bug 12345” or a direct link to the bug as viewed in a browser. When a test with a failure note like this fails, the test artifacts will include a note, bug number, link or other vector that can significantly speed triage and resolution.

The next post

Has some notes on organization, structure and design for data-driven tests.

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