Unit Testing A Database

In a recent job interview I was asked the question regarding Unit Testing/Automated Testing of a Database? An interesting question and indeed an interesting problem. I thought it was a good topic to describe what I’ve done in the past, and where I would go for a more complete testing environment given the opportunity of a entire XP project.

This is the approach I have implemented successfully in the past. It’s not a complete solution, however at the time with the client it provided appropriate coverage.

I don’t use a framework such as dbUnit to load data via XML, or specifically test data. XML is ugly to store data, and also with maintenance and comparison. I start with a pre-configured database of representative sample data, refer to my notes later on this, and then I use the tests of the application to perform the necessary data manipulation. This ensures that you are as close as possible to testing actual situations, and ensuring that any issues the application does (such as enter bad data, or RI failures) are caught appropriately.

Within this process an automated build test would first reset the database to a known set of data. I’ve also found that this helps as you can also recreate the schema if necessary. As part of Schema Design in an XP Development, I have two ways to create the database schema. You can create it from scratch (so there is always appropriate SQL to create the current version of the Schema, lets say BUILD_102. Alternatively, you can always upgrade between releases, for example between BUILD_101 and BUILD_102 with the appropriate upgrade scripts. Upgrade or patch scripts only move one version to the next version. It’s not possible in a production environment to simply recreate your schema for each release, however for testing and training you can. It’s also pointless after 50 releases to have to perform 50 patch releases from the original source schema for every automated build test.

This does lead to two paths necessary for creating a schema, but this can also be tested adequately in an automated way.

I also split my application tests suites that use the sample data into two buckets. Destructive and Non-Destructive. The reason is the Non-Destructive tests (i.e., non DML statements) can be re-run as many times as necessary. The Destructive tests (i.e., DML statements) can only be run once, before the database must be restored. Of course you can have the approach of setUp() and tearDown() within JUnit however it’s cleaner if you can extract this somewhat to a higher level, making the Unit Tests easier. By also running tests that don’t continually use the some data, or builds the data though test execution, you get a better coverage of different data sets. To give a few examples, You could create a Test that created a row of data, then edited the same row, then deleted the row. These are indeed valid, but if the first test fails, how do you know if the update and delete tests are also broken, they are by dependant by default and will fail, but did they really. If with your sample data, you created a new row, edited a different pre-configured row, and also deleted a different pre-configured row, you could eliminate the need to dependencies.

Now of course, there are situations where data must be specifically checked at the database level, for example it may never be displayed in your application, it may be intermediate information that is then summarised for display, or internal audit information held against data (for example Create User, Last Updated User), or data created by procedures or triggers. There are also situations when even within an application testing that can verify the data in a User Interface, you want to verify this at the source.

To this end I have a custom written JUnit extension that can perform specific SQL statements and comparison. I’ll need to write about this and provide this at a later time. (when I can dig it up)

Sample Data

Sample Data in the database is pre-configured, not in XML files, but so it can be managed by more primitive means, either by a database GUI interface or via SQL flat files or even text files. Why have pre-configured data this way? A few reasons.

  • It’s not coupled to your tests in any way, so it can be reused, for example as Training Data.
  • You can use database specific tools more easily say in loading the data in a relational way.
  • You can use the same database specific tools to export the data easily, if say you use an application to modify certain information.
  • You could more easily incorporate legacy data that is also being migrated if you use the same database specific tools.

Granted XML is universal in it’s data representation, it’s more self descriptive, but it’s a really pain to edit manually, and it’s very verbose when there are simply more primitive methods of this type of data management.

So we are creating a pre-configured data set, and an extensive one when possible. As I mentioned, the re-use capabilities for training or demonstrations really works.

Training Data

I have successfully with a number of systems, specifically CRM implementations used a Cartoon Environment for the sample data. There are a few reasons for this. First, most people I’ve ever met can related in some way to some set of the data. If they can’t, then there can read info online, or watch a movie etc, and get an appreciation from the representative data set, effectively I’m leveraging of the time and effort of others here, much better then a non-descript set of data.

You have the cartoon characters (e.g. Mickey Mouse, Donald Duck, Daffy Duck, Marvin the Martian, The Simpsons, The Flintstones, The Jetsons), use all the streets and rides as Disneyland as addresses, the animators as the users (e.g. Walt Disney, Chuck Jones, Stan Lee), you can use the different studios (e.g. Warner Bros, Disney, Pixar) for different states or countries, you can use shows or movies (e.g. Toy Story, Shrek) to group characters in other ways.

With this type of data, common attributes such as birth date, family units, nick names, people deceased etc, are all part of the available data. It’s surprising how much information you can find when using The Simpsons for example, of full names, addresses, interests etc.

It’s impressive when the CEO of a company is showing the application to overseas business partners, when his knowledge of the application (from his management perspective) is sufficient, there is no knowledge of the data really necessary to use or explain as it’s commonly used and generally understood.

At this point I would like to ensure that I correctly acknowledge the registered trademarks of Disney, Warner Bros, Hanna Barbera, Pixax, Dreamworks and that I am not using the names for any profit.


So this is what I’ve used in the past. What would I do in the future if I was charged with bullet proof testing of a database, even independent of an application, effectively 100% test coverage of the data. Well, this is an unproven approach, but I’d relish the opportunity to give it a full blooded test one day.

How to test the database with an automated test approach.

I’d consider the breaking down of testing into 3 areas. These being:

  1. Schema
  2. Data
  3. Business Logic/Referential Integrity

Each of this is effectively built on the the preceding points.


This would be quite straight forward it’s a flat comparison between schema’s, which could be managed via the appropriate products data dictionary tables using SQL. You could even simply compare 2 schema’s in a few simple SQL statements. You could also use the approach of export the schema definition, and then compare flat files. You will find some downsides to these approaches, ordering is a big thing, columns within a database table, or the order of the tables that are exported may not be guaranteed. However given appropriate standards are defined used of tools this comparison could easily occur.

Being able to verify patches between releases, and full installed schema’s are also possible. The schema is the easy part.


Data could be tested in varying means. Counts, sums and sample comparisons, but it’s also just data, why not md5sum the entire data. Why not even dump the data to flat files, and use basic difference tools for comparison. One simple approach. Especially if you are loading data, using or manipulating it, then you can export and compare at a file level. This would work very well for data considered Read Only for the life of testing.
This format may allow you to compare data between two different database products, e.g. Oracle use for your transactional online processing, and MySQL use for Web Data or Management Summary Reporting application.

In order to test the data you need the schema, but how can you test the data without the business logic and Referential Integrity. Within MySQL you can easily disable foreign key constraints, or easily adjust the table type to a structure to ignore this syntax. This could allow you to run tests with and without Referential Integrity to determine the strength of your application.

Of course this is a static version of the data. Performing separate testing of DML statements directly against the database could prove a waste of time, unless your application was written in such a way, that your application database layer was a complete API. Still you would be simulating what your application is ultimately doing, so it could be overkill. You could apply the techniques of comparison with know results after a successful running of automated build testing.

Business Logic/Referential Integrity

The hard stuff. Well you could be half way there with adequate schema and data testing. At least you are then confident that core integrity exists.

The problem is also to do with application integrity verses database integrity.

Let’s take a percentage, it goes from 0 to 100. Now using MySQL for example, you would define this as TINYINT(3) UNSIGNED, giving you a valid range of 0-255, and by default a display characteristic of 3 characters (the (3) in this example is just beautification).

You application logic restricts the value into this column to 0 to 100. But do you enforce this at the database? Depends on your needs. If the application is the only way to insert and maintain data, then you could get away with it, if data can be managed from other external systems, you may have APIs that also need to manage it. What if you grant SQL access to DBA’s, could they accidentially mess it up. That song “It’s a fine line between pleasure and pain” comes to mind at this moment. I guess what I’m getting at here, in solely database testing you could easily insert 255 into a percent column and pass a number of data specific tests. I’d assume it would fail some as well otherwise your tests aren’t complete, but when using the application you could never test 255, as the client would never allow it.

There are a lot more issues in RI testing, Cascading UPDATE, DELETE rules for etc. And then when you work all that out, you have to start with Triggers and Stored procedures. I’m not going to spend any time here at this time.

Unforeseen Side Effects

Data is a strange beast. It’s the source of information, so I always like to go back to the data for comparison, however the lack of good data (most notably Legacy Systems Migration) can drive you mad. What good is it to have a new system but not be able to enforce an adequate level of Referential Integrity or Business logic due to incomplete historical data. In essence this has proven in the time I’ve also supported large systems, a good portion of the development cost in support, it’s bad data and/or the need for a simple application to have more complex rules to cater for so called incomplete data.

I’ll give you a trivial example. Gender. In the new system an organisation will always ensure they get the gender of a customer (let’s not wonder how they do it, it’s just an example). So the application is designed to support Male/Female, Reference Data may exist to translate M & F to Male and Female respectively for data storage efficiency. Check constraints, enumeration data types (which I don’t like) may exist. Reports may do side by side comparisons.

Now the company buys a competitor, and then gets their database of 500,000 customers, but they don’t record the Gender. Do you then relax all your great integrity? Do you introduce a gender of Unknown? But that’s only for display, the maintenance screens can’t allow you to select it, so you then need a different level of Reference Data management. Do you make an educated guess and correct the data? Does the customer do an expensive mailout campaign and data collection process to correct this information? So what’s the big deal anyway the customer asks? Well if it’s an organisation that sells hygiene products, you don’t want to sending out material on Shaving Cream to Women on your list and Body Wax to Men. However you can’t use that explanation to describe solely a database driven reason to the customer for the cost of introducing this data. How do you show business value to the customer, when they simply what the data available?

I know this is a trivial example, but if I had a dollar for every trivial problem that customers spent months on,verses the really hard problems, I be writing this from a much more comfortable and relaxing resort haven. (A ski resort rather then a beach resort)


So can you Unit Test a Database solely without an application? Yes. Would you want to? Maybe, to a certain degree. Depending on your type of data. If all your information is highly visible in data entry and data retrieval, you should couple testing more closely with your application. If your data is very generated and collated, rarely user entered but bulk loaded, such as Sensis information or GIS information, then dedicated testing all aspects of the database decoupled from the application could indeed make your application test easier, because it’s easier to identify bad data that the application creates.