Added WasteRepository unit tests

src/test/java/ntnu/idatt2016/v233/SmartMat/repository/group/WasteRepositoryTest.java

+package ntnu.idatt2016.v233.SmartMat.repository.group;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.autoconfigure.orm.jpa.DataJpaTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+import java.sql.Timestamp;
+import java.time.LocalDateTime;
+import java.util.List;
+import java.util.Optional;
+
+import ntnu.idatt2016.v233.SmartMat.entity.Waste;
+import ntnu.idatt2016.v233.SmartMat.repository.group.WasteRepository;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+@ExtendWith(SpringExtension.class)
+@DataJpaTest
+class WasteRepositoryTest {
+
+    @Autowired
+    private WasteRepository wasteRepository;
+
+    private Waste waste1;
+    private Waste waste2;
+
+    @BeforeEach
+    void setUp() {
+        waste1 = Waste.builder()
+                .groupId(1L)
+                .ean(123456L)
+                .timestamp(Timestamp.valueOf(LocalDateTime.now()))
+                .amount(10)
+                .unit("kg")
+                .build();
+
+        waste2 = Waste.builder()
+                .groupId(1L)
+                .ean(789012L)
+                .timestamp(Timestamp.valueOf(LocalDateTime.now()))
+                .amount(5)
+                .unit("kg")
+                .build();
+
+        wasteRepository.save(waste1);
+        wasteRepository.save(waste2);
+    }
+
+    @Test
+    void findByGroupId() {
+        Optional<List<Waste>> result = wasteRepository.findByGroupId(1L);
+
+        assertTrue(result.isPresent());
+        assertEquals(2, result.get().size());
+        assertEquals(waste1.getEan(), result.get().get(0).getEan());
+        assertEquals(waste2.getEan(), result.get().get(1).getEan());
+    }
+}