What you need to do to add tests is you need to create another directory called test within the root src package.
This is how the root looks like.
src
main
java
org.example
app
service
ClientService <----- this is where your code logic is for the customer
To create a test class for the CustomerService you need to create the same package structure but under a new test package:
src
main
test <-----------------this the new package
java
org.example
app
service
CustomerServiceTest <----- this is where you create the test class and it must have Test at the end
Within the test class you must add simple unit tests for the methods within the CustomerService class in this CustomerServiceTest class
What you need to do to add tests is you need to create another directory called test within the root src package. This is how the root looks like.
src main java org.example app service ClientService <----- this is where your code logic is for the customer
To create a test class for the CustomerService you need to create the same package structure but under a new test package:
src main test <-----------------this the new package java org.example app service CustomerServiceTest <----- this is where you create the test class and it must have Test at the end
Within the test class you must add simple unit tests for the methods within the CustomerService class in this CustomerServiceTest class