Hi,
The use case is from a previous question...
https://community.smartbear.com/discussions/readyapi-questions/assertions/262648/Assertions | SmartBear Community
In ArmyGrads Groovy snippet, the assertion isn't required for the use case. But I can see why Rao added it for his demo to show that the value can be found.
For ArmyGrads example to work, you need use Get Data to pull in the required value from the datasource step and assign it the var datasourceBook1 prior to the IF statement.
Something like...
def datasourceBook1 = context.expand( '${CustomerDataSource#Book1}' );
Then you should both the response value and datasource values.