Why I always get "No tests were found" "Class not found: xxx" when running the defualt local unit ExampleUnitTest class on Android?

I'm trying to use Unit testing using JUnit in my android project, so I tried to run the ExampleUnitTest class in the (test) folder with this statement:

Assert.assertEquals(4,5)

and it passed I don't know why then I created another class in the same folder and now I get the error even on the ExampleUnitTest class

No tests where found with a message Class not found: "{{packageName}}.ExampleUnitTest"

This is the ExampleUnitTest class ExampleUnitTest class

This is the configuration ExampleUnitTest configuration

Using this dependency:

testImplementation 'junit:junit:4.13.2'