Will it work?
I guess you should add services also in matrix.

matrix:
  - SQL: mssql2008r2sp2
   mssql_jdbc_test_connection_properties: jdbc:sqlserver://localhost:1433;instanceName=SQL2008R2SP2;databaseName=master;username=sa;password=Password12!;
  - SQL: mssql2016
   mssql_jdbc_test_connection_properties: jdbc:sqlserver://localhost:1433;instanceName=SQL2016;databaseName=master;username=sa;password=Password12!;

I did not check this but definitely you want matrix of services too.

Ref: https://stackoverflow.com/questions/42690548/multiple-combinations-of-python-and-sql-server-on-appveyor

Also please note that all MS SQL servers use the same default port 1433. Therefore please start and stop them sequentially to avoid port conflicts. To allow all SQL Server instances to be started simultaneously, please run this script at init stage.

Ref: https://www.appveyor.com/docs/services-databases/

Hello @nsidhaye Hope you are doing well! from my investigation, matrix does not support services. Before I create this PR, I tested it in my personal fork and it worked this way. Thank you for sharing the link, I definitely will try it! If it works I will update my PR. Thank you :)

thank you @nsidhaye for sharing the link! I didn't find this link when I was doing investigation. I really love the idea to specify variables in matrix and then use CMD to start services! I updated my PR. Thank you for knowledge sharing!