Cover Example Tests

In this article we show both the input source and the Cover generated tests for code of varied complexity accompanied by a detailed narrative to help you further understand tests generated by Cover.



1. Basic assertions

This is a simple example of Spring Service source code with a trivial getter. Dcover can write a Spring Boot test for the getter in a service provider by inlining Arrange, Act, and Assert.

1.1 Source

import org.springframework.stereotype.Service;

@Service
public class SimpleService
{
  public String getValue() {
    return "a really simple service";
  }
}

1.2 Test generated by Diffblue Cover

@SpringBootTest
@RunWith(org.springframework.test.context.junit4.SpringRunner.class)
public class SimpleServiceDiffblueTest {
  @Autowired
  private SimpleService simpleService;
  @Test
  public void testGetValue() {
    // Arrange, Act and Assert
    assertEquals("a really simple service", this.simpleService.getValue());
  }
}

2. Mocking

This is a class that contains two methods to upload and download a file to/from Amazon S3 bucket. As the Amazon S3 bucket is a cloud storage mechanism, the test for this class/methods requires dependency injection. Dcover can mock these types of dependencies and tests downloadFileFromBucket method by asserting the expected S3Object and the downloaded S3Object using the method.

2.1 Source

@Service
public class AmazonService {

  @Autowired
  private AmazonS3 s3client;

  public PutObjectResult uploadFileToBucket(String bucketName, String key, File file) {
    return s3client.putObject(bucketName, key, file);
  }

  public S3Object downloadFileFromBucket(String bucketName, String key) {
    return s3client.getObject(bucketName, key);
  }
}

2.2 Tests generated by Diffblue Cover

@SpringBootTest
public class AmazonServiceDiffblueTest {
  @MockBean
  private AmazonS3Client amazonS3Client;
  @Autowired
  private AmazonService amazonService;
  @Test
  public void testUploadFileToBucket() {
    // Arrange
    PutObjectResult putObjectResult = new PutObjectResult();
    putObjectResult.setContentMd5("file-hash");
    when(this.amazonS3Client.putObject(or(isA(String.class), isNull()), or(isA(String.class), isNull()),
        or(isA(File.class), isNull()))).thenReturn(putObjectResult);

    // Act and Assert
    assertSame(putObjectResult, this.amazonService.uploadFileToBucket("foo", "foo",
        Paths.get(System.getProperty("java.io.tmpdir"), "test.txt").toFile()));
  }
  @Test
  public void testDownloadFileFromBucket() throws UnsupportedEncodingException {
    // Arrange
    StringInputStream objectContent = new StringInputStream("file-name");
    S3Object s3Object = new S3Object();
    s3Object.setObjectContent(objectContent);
    when(this.amazonS3Client.getObject(or(isA(String.class), isNull()), or(isA(String.class), isNull())))
        .thenReturn(s3Object);

    // Act and Assert
    assertSame(s3Object, this.amazonService.downloadFileFromBucket("foo", "foo"));
  }
}

3. OS agnostic assertions

This example returns time in a different format. Dcover writes a test to assert date and time that is not dependent on operating system or local time zones.

3.1 Source

public class TimeInAliceWonderland {

  private static final String DODO_DATETIME_FORMAT = "ss:mm:HH dd-MMM-yyyy";

  public static String reformatDodoDateTime(Date humanDate) {
    Map<String, DateFormat> dateFormatMap = new HashMap<>();
    dateFormatMap.put(DODO_DATETIME_FORMAT, new SimpleDateFormat(DODO_DATETIME_FORMAT));
    return dateFormatMap.get(DODO_DATETIME_FORMAT).format(humanDate);
  }
}

3.2 Test generated by Diffblue Cover

@Test
  public void testReformatDodoDateTime() {
    LocalDateTime atStartOfDayResult = LocalDate.of(1970, 1, 1).atStartOfDay();
    assertEquals("00:00:00 01-Jan-1970", TimeInAliceWonderland
        .reformatDodoDateTime(
            Date.from(atStartOfDayResult.atZone(ZoneId.systemDefault()).toInstant())));
  }

4. Example containing logic

In this example, Dcover writes two tests to cover each pathway through the conditional - a test which adds 10 to the balance and asserts the new balance should be 20 and a second test where the account is closed.

4.1 Source

public class Account {
  private final long accountNumber;
  private final Client client;
  private long currentBalance;
  private String accountName;
  private AccountState accountState;

  public Account(final long accountNumber, final Client client, final long amount) {
    this.accountNumber = accountNumber;
    this.client = client;
    currentBalance = amount;
    accountName = "Current";
    accountState = AccountState.OPEN;
  }

  public long getCurrentBalance() {
    return currentBalance;
  }

  public void addToBalance(final long amount) throws AccountException {
    if (getAccountState() != AccountState.OPEN) {
      throw new AccountException("Cannot add to balance, account is closed.");
    }
    currentBalance += amount;
  }

4.2 Test generated by Diffblue Cover

 @Test
  public void testAddToBalance() throws AccountException {
    // Arrange
    Account account = new Account(1234567890L, new Client("Carlos Welch"), 10L);

    // Act
    account.addToBalance(10L);

    // Assert
    assertEquals(20L, account.getCurrentBalance());
  }

5. Example of complex logic

This example code has 3 branches - Dcover covers 100% of branches and creates three tests for three cases using existing enum values.

5.1 Source

public class VirtualSnackCupboard {

  public static Snack whatCanISnackNow(int oClock) {
    if (oClock == 10) {
      return Snack.CHOCOLATE;
    } else if (oClock == 15) {
      return Snack.CAKES;
    } else {
      return Snack.VEGGIE;
    }
  }
  enum Snack {VEGGIE, CHOCOLATE, CAKES}
}

5.2 Tests generated by Diffblue Cover

  public void testPickSnack() {
    assertEquals(VirtualSnackCupboard.Snack.CHOCOLATE, VirtualSnackCupboard.whatCanISnackNow(10));
    assertEquals(VirtualSnackCupboard.Snack.CAKES, VirtualSnackCupboard.whatCanISnackNow(15));
    assertEquals(VirtualSnackCupboard.Snack.VEGGIE, VirtualSnackCupboard.whatCanISnackNow(0));

As can be seen, Diffblue Cover can generate tests for a wide variety of code scenarios - we encourage you to try out Cover CLI and Cover IntelliJ Plugin for yourself to learn more.

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