Added and rewrote tests

src/test/java/de/rwu/easydrop/service/writer/TransactionWriterTest.java

@@ -0,0 +1,63 @@
+package de.rwu.easydrop.service.writer;
+
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.verifyNoInteractions;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import de.rwu.easydrop.api.dto.TransactionDTO;
+import de.rwu.easydrop.data.connector.TransactionPersistenceInterface;
+import de.rwu.easydrop.exception.InvalidTransactionException;
+import de.rwu.easydrop.model.Transaction;
+import de.rwu.easydrop.service.mapping.TransactionMapper;
+
+class TransactionWriterTest {
+
+    @Mock
+    private TransactionPersistenceInterface persistence;
+
+    private TransactionWriter writer;
+
+    @BeforeEach
+    void setUp() {
+        MockitoAnnotations.openMocks(this);
+        writer = new TransactionWriter(persistence);
+    }
+
+    @Test
+    void writeTXToPersistence_ValidTransaction_TransactionSaved() {
+        // Arrange
+        Transaction transaction = new Transaction();
+        transaction.setOfferId("123");
+        transaction.setVolume(123f);
+        transaction.setEarnings(12.23);
+        transaction.setTransactionTime("2020-01-01 00:00:00");
+
+        TransactionDTO expectedDTO = TransactionMapper.mapTXToDTO(transaction);
+
+        // Act
+        writer.writeTXToPersistence(transaction);
+
+        // Assert
+        verify(persistence).writeTX(expectedDTO);
+    }
+
+    @Test
+    void writeTXToPersistence_InvalidTransaction_ValidationExceptionThrown() {
+        // Arrange
+        Transaction transaction = new Transaction();
+        transaction.setVolume(123f);
+        transaction.setEarnings(12.23);
+        transaction.setTransactionTime("2020-01-01 00:00:00");
+
+        // Act & Assert
+        assertThrows(InvalidTransactionException.class, () -> writer.writeTXToPersistence(transaction));
+
+        // Verify that persistence.writeTX is not called
+        verifyNoInteractions(persistence);
+    }
+}