test: Add H2 database for testing and update config

src/main/resources/application-test.properties

@@ -0,0 +1,5 @@
+spring.datasource.url=jdbc:h2:mem:testdb;DB_CLOSE_DELAY=-1
+spring.datasource.driver-class-name=org.h2.Driver
+spring.datasource.username=sa
+spring.datasource.password=
+spring.jpa.database-platform=org.hibernate.dialect.H2Dialect

src/test/java/de/szut/lf8_starter/Lf8StarterApplicationTests.java

@@ -2,6 +2,7 @@ package de.szut.lf8_starter;
 
 import org.junit.jupiter.api.Test;
 import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.TestPropertySource;
 
 @SpringBootTest
 class Lf8StarterApplicationTests {