There are several reasons why you need to develop a comprehensive testing strategy for your RDBMS:
Here are some interesting questions for people not convinced of the need for database testing:
I think that one of the reasons that we don’t hear much about database testing is because it is a relatively new idea within the data community. Many traditional data professionals seem to think that testing is something that other people do, particularly test/quality assurance professionals, do. This reflects a penchant for over-specialization and a serial approach towards development by traditionalists, two ideas which have also been shown to be questionable organizational approaches at best.
Figure 1 indicates what you should consider testing when it comes to relational databases. The reflects the context of a single database, the dashed lines indicate threat boundaries, indicating that you need to consider threats both within the database (internal testing) and at the interface to the database (interface/black box testing). For details, read the article What To Test in a Database.
Figure 1. What to test in a database (click to enlarge).
Automated database regression testing is the act of running a test suite on a regular basis, ideally whenever a developer or data engineer has done something which could potentially inject a defect into the implementation of a database. For details, please read Database Testing: Automated Database Regression Testing.
During development cycles, the primary people responsible for doing database testing are application developers and Agile data engineers. They will typically pair together, and because they are hopefully taking a TDD-approach to development the implication is that they’ll be doing database unit testing on a continuous basis. During the release cycle your testers, if you have any, will be responsible for the final system testing efforts and therefore they will also be doing database testing.
The role of your data management (DM) group, or IT management if your organization has no DM group, should be to support your database testing efforts. They should promote the concept that database testing is important, should help people get the requisite training that they require, and should help obtain database testing tools for your organization. Database testing is something that is done continuously by the people on development teams, not something performed by another group (except of course for system testing efforts). In short, the DM group needs to support database testing efforts and then get out of the way of the people who are actually doing the work.
Database testing is new to many people, and as a result you are likely to face several challenges:
In general, I highly suggest that you read my article Adopting Evolutionary/Agile Database Techniquesand consider buying the book Fearless Change which describes a pattern language for successfully implementing change within organizations.
A common quality technique is to use data inspection tools to examine existing data within a database. You might use something as simple as a SQL-based query tool such as DB Inspect to select a subset of the data within a database to visually inspect the results. For example, you may choose to view the unique values in a column to determine what values are stored in it, or compare the row count of a table with the count of the resulting rows from joining the table with another one. If the two counts are the same then you don’t have an RI problem across the join.
As Richard Dallaway points out, the problem with data inspection is that it is often done manually and on an irregular basis. When you make changes later, sometimes months or years later, you need to redo your inspection efforts. This is costly, time consuming, and error prone.
Data inspection is more of a debugging technique than it is a testing technique. It is clearly an important technique, but it’s not something that will greatly contribute to your efforts to ensure data quality within your organization.
Agile software developers take a test-first approach to development where they write a test before you write just enough production code to fulfill that test. Figure 3 depicts the steps of test first development (TFD). The first step is to quickly add a test, basically just enough code to fail. You then update your functional code to make it pass the new test. The third step is to run your tests again. If they fail you need to update your functional code and retest. Once the tests pass you iterate and add another test.
Figure 3. The process of Test First Development (TFD) – Click to enlarge.
The steps of Test-First Development (TFD)
Test-driven development (TDD) is an evolutionary approach to development which combines test-first development and refactoring. When an agile software developer goes to implement a new feature, the first question they ask themselves is “Is this the best design possible which enables me to add this feature?” If the answer is yes, then they do the work to add the feature. If the answer is no then they refactor the design to make it the best possible then they continue with a TFD approach. This strategy is applicable to developing both your application code and your database schema, two things that you would work on in parallel.When you first start following a TDD approach to development you quickly discover that to make it successful you need to automate as much of the process as possible? Do you really want to manually run the same build script(s) and the same testing script(s) over and over again? Of course not. So, agile developers have created OSS tools such as ANT, Maven, and Cruise Control (to name a few) which enable them to automate these tasks. More importantly, it enables them to automate their database testing script into the build procedure itself.Agile developers realize that testing is so important to their success that it is something they do every day, not just at the end of the lifecycle, following agile testing strategies. They test as often and early as possible, and better yet they test first.
I’d like to share a few database testing “best practices” with you:
Isn’t it time that we stopped talking about data quality and actually started doing something about it?
