If you write code to SQL Server then you might be interested in this: at the end of 2017 I wrote a tSQLt tdd training course which has helped over 300 people learn both tSQLt and how to apply TDD practices to their SQL Server T-SQL development, you can join the course at https://courses.agilesql.club. The course is free if you are happy to wait 10 weeks to complete it, with 1 lesson being made available per week - if you are in more of a hurry or you would like to help support the project you can purchase the course which makes it instantly available to you.
In the spirit of having apps that do just one thing I have put a really small .net app on github that tries to create a connection to a SQL Server database and just keeps retrying until it is available:
If you have a CI build and you start a new instance or database or azure db etc it can take different amounts of time to be available so this just sits trying until it can get a valid connection and you can continue your CI loveliness.
This can easily be replicated using powershell but it isn’t always available.
To use it do something like:
-S server -E -T 600
-S server -U user -P password -T 600