Setup unit tests and implements test for the token limit and trivial tests for userRepository

backend/src/test/resources/application.properties

@@ -0,0 +1,3 @@
+spring.datasource.driver-class-name=org.testcontainers.jdbc.ContainerDatabaseDriver
+spring.jpa.hibernate.ddl-auto=create-drop
+spring.jpa.database-platform=org.hibernate.dialect.PostgreSQLDialect