Flyway and tSQLt – migrating to warmer test climates

“If you truly have faith in your convictions, then your convictions should be able to stand criticism and testing.”
DaShanne Stokes

Welcome fellow TestDriven-Development enthusiasts… is what I would say if i actually ever did TDD and didn’t just, you know… write regular unit tests after the fact instead.

I’m going to be honest, I love the idea of TDD but have I ever actually been able to do it? No. Have competent developers been able to do it successfully? Yes, of course. Don’t know anything about TDD? You’re in luck! Click here for an introduction (don’t worry though, THIS post is not going to be about TDD anyway, so you can also keep reading).

But one thing we can all agree on is that testing is pretty important. Testing has evolved over the years though and there are a million-and-one ways to test your code, but one of the most difficult and frustrating things to test, from experience, is database code.

gilmore girls shot of cynicism GIF

Some people argue that the days of testing, indeed, the days of stored procedures themselves are gone and that everything we do in databases should be tested using a combination of different logic and scripting languages like Python or PowerShell… but we’re not quite there yet, are we?

Fortunately though we’re not alone in this endeavor, we have access to one of the best ways to test T-SQL code: tsqlt. You can read more about tsql at the site here but in short – we have WAYS to test your SQL Server* code. The only problem is, when you’re using a migrations approach… how?

*There are also many ways to unit test code from other RDBMS’ of course, like utPLSQL for Oracle Database or pgTAP for PostgreSQL – would this method work for those? Maybe! Try adapting the method below and let me know how you get on!

I’ve already talked about how implementing tests is easier for state based database source control in a previous post because we can easily filter tests out when deploying to later stage environments, however with migrations this can be a real pain because you have to effectively work on tests like you would any normal database changes, and maybe even check them in at the same time – so ultimately, they should be managed in the same way as database schema migrations… but we can’t filter them out of migrations or easily pick and choose what migrations get run against test and Prod, without a whole lot of manual intervention.

Basically. It’s a mess.

mess fail GIF

But during my last post about Flyway I was inspired. This simple and easy to use technology just seems to make things really easy and seemingly has an option for EVERYTHING, so the question I started asking myself was: “How hard would it be to adapt this pipeline to add unit tests?” and actually although there were complications, it was still easier than I thought it would be! Here’s how you can get up and running with the tSQLt framework and Flyway migrations.

1 – Download the scripts to create the tSQLt framework and tests from the site

Ok this was the easiest step of them all, largely because in the zip file you download from the tsqlt website all you have is a set of scripts, first needed to enable CLR and the second to install the tsqlt framework:

As part of my previous pipeline I’m actually using Azure SQL Database as my development environment, where RECONFIGURE is not a supported keyword and where we don’t need to run the CLR script anyway, so all I needed was the tSQLt.class.sql file.

The good thing about this is that we can copy it across into a migration and have this as our base test class migration, and then any tests we write on top of it will just extend it – so as long as we remember to update it _fairly_ frequently with any new tsqlt update, we should be fine! (Flyway won’t throw an error because these are non persistent build objects, so no awkward checksum violations to worry about!)

2 – Adapt the folder structure in the repository for tests

I added 2 new folders to my _Migrations top level folder, a Schema_Migrations folder and a Test_Migrations folder. When you pass Flyway a location for migrations, it will recursively scan folders in that location looking for migrations to run in order. I copied the migrations I had previously into the Schema Migrations folder and then my new tSQLt creating migration into the Test Migrations folder. This allows them to be easily coupled by developers, whether you’re writing unit tests or practicing TDD:

You’ll have noticed I called my base testing migration V900__ – this is because I do still want complete separation and if we have a V5 migration in schema migrations and a V5 testing migration, we’re going to have some problems.

3 – Add a callback to handle removal of the objects

As I was putting this together, I noticed that I could use flyway migrate to run the tSQLt framework against my Dev database, but every time I tried to then flyway clean that database I got a very nasty error stating that the tSQLt assembly could not be removed because of dependent objects.

Flyway does not handle complex dependencies very well unfortunately, that’s where you’d use an industry leading comparison tool like SQL Compare so, with some advise from teh wonderful Flyway team, I set to work on a callback. A callback is how you can hook into Flyway’s own processes, telling it to do something before, during or after certain commands. In my case we were going to remove all of the tSQLt objects prior to running Flyway clean to remove the rest of the schema. To make it future proof (in case objects are added or removed from the tSQLt framework), I wrote a couple of cursors to go through the different objects that were dependent on the assembly and remove them, rather than generating a script I know to have all of the tSQLt objects in right now. You can find the code for the callback in my GitHub here, you are welcome to it!

Animated GIF

All you have to do is name it beforeClean.sql and ensure it is in the directory with your other sql migrations so that it will pick this up and run it – I put it in my Test_Migrations folder, because I only want it to run this callback when cleaning the build DB, as this is the only place we’re utilizing automated unit tests… for now!

4 – Update the Azure DevOps pipeline

I’ve got my callback, I’ve got my tSQLt migration and the folder structure is all correct and is pushed to Azure DevOps but naturally it is breaking the build *sad* but fortunately all we now have to do is update the YAML pipeline file:

- master

  vmImage: 'ubuntu-latest'

- task: DockerInstaller@0
    dockerVersion: '17.09.0-ce'
  displayName: 'Install Docker'

- task: Bash@3
    targettype: 'inline'
    script: docker run -v $(FLYWAY_LOCATIONS)/Test_Migrations:/flyway/sql -v $(FLYWAY_CONFIG_FILES):/flyway/conf flyway/flyway clean -enterprise
  displayName: 'Clean build schema'

- task: Bash@3
    targettype: 'inline'
    script: docker run -v $(FLYWAY_LOCATIONS)/Schema_Migrations:/flyway/sql -v $(FLYWAY_CONFIG_FILES):/flyway/conf flyway/flyway migrate -enterprise
  displayName: 'Run flyway for schema'

- task: Bash@3
    targettype: 'inline'
    script: docker run -v $(FLYWAY_LOCATIONS)/Test_migrations:/flyway/sql -v $(FLYWAY_CONFIG_FILES):/flyway/conf flyway/flyway migrate -enterprise
  displayName: 'Run flyway for tSQLt'

You will notice a couple of important things that I have highlighted above:

  1. I’m cleaning the build schema using the Test_Migrations repository – this is because that is where my callback is and I need that to run before the clean otherwise it will fail due to the tSQLt assembly issue (line 17)
  2. I am running the migrate for the tests and the schema separately in the file, instead of just calling flyway to recursively run everything in the _Migrations folder. This is because I want them to be 2 separate steps, in case I need to modify or remove either one of them, or insert other steps in between and so that I can see the testing output in a separate stage of the CI pipeline (lines 23 and 29).

Caveat: As a result of (Option 2) running the 2 processes separately, it means running Flyway twice but specifying the Schema_Build and Test_Build folders in the YAML as being mapped to Flyway’s sql directory (lines 16 and 22 in the file above) but the problem this causes is that the second time Flyway runs, when it recursively scans the Test_Migrations folder it will not find the migrations that are present in the Flyway_Schema_History table, resulting in an error as Flyway is unable to find and resolve the migrations locally.

The way to fix this though is pretty simple – you find the line in the Flyway Config file that says “IgnoreMissingMigrations” which will allow it to easily continue. We wouldn’t have to worry about this setting though, if we were just recursively looking to migrate the Schema and Test migrations in the same step (but I’m a control freak tee-hee).

Now, once committed this all runs really successfully. Velvety smooth one might even say… but we’re not actually testing anything yet.

5 – Add some tests!

I’ve added a single tSQLt test to my repository (also available at the same GitHub link), it was originally created by George Mastros and is part of the SQLCop analysis tests – checking if I have any user procedures named “SP_”, as we know that is bad practice – and I have wrapped it up in a new tSQLt test class ready to run.

You’ll notice I also have a V999.9__ migration in the folder too, the purpose of this was to ‘top and tail’ the migrations; first have a script to set up tSQLt that could be easily maintained in isolation and then end with a script that lets me do just 1 thing: execute all of the tests. You can do this by simply executing:


and we should be able to capture this output in the relevant stage of the pipeline.

Some of you may be asking why I chose to have the run unit tests as part of the setting up of the testing objects – this was because I had 2 options:

  1. I’m already executing scripts against the DB with Flyway, I may as well just carry on!
  2. The only other way I could think to do it was via a PowerShell script or run SQL job in Azure DevOps but the 2 plugins I tried fell over because I was using a Ubuntu machine for the build.

So naturally being the simple person I am, I opted for 1! But you could easily go for the second if you prefer!

6 – Test, Test, Test

Once you’ve handled the setup, got the callback in place (and also followed the steps from the last blog post to get this set up in the first place!) you should be able to commit it all these changes and have a build that runs, installs tSQLt and then runs your tests:

I realize there are a lot of “Warnings” in there, but that is just Azure DevOps capturing the output, the real part of this we’re interested in is lines 31-40 and if we clean up the warnings a little you’ll get:

|Test Execution Summary|
|No|Test Case Name|Dur(ms)|Result |
|1 |[somenewclass].[testProceduresNamedSP_]|144|Success|
Test Case Summary: 
1 test case(s) executed, 1 succeeded, 0 failed, 0 errored. 

But if I introduce a migration to Flyway with a new Repeatable Migration that creates a stored procedure named SP_SomeNewProc…

|Test Execution Summary|
|No|Test Case Name|Dur(ms)|Result |
|1 |[somenewclass].[testProceduresNamedSP_]|184|Failure|
Test Case Summary: 
1 test case(s) executed, 0 succeeded, 1 failed, 0 errored. 

It even tells us the name of the offending sproc:

All I have to do now is make the corresponding change to remove SP_ in dev against a bug fix branch, push it, create a PR, approve and merge it in and then boom, the build is right as rain again:

Thus bringing us back into line with standard acceptable practice, preventing us from delivering poor coding standards later in the pipeline and ensuring that we test our code before deploying.


Just because you adopt a more agile, migrations based method of database development and deployment, doesn’t mean that you have to give up on automated testing during Continuous Integration, and you can easily apply these same principles to any pipeline. With just a couple of tweaks you can easily have a fully automated Flyway pipeline (even xRDBMS) and incorporate Unit Tests too!