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1. Introduction

Unlike other Spring-based applications, testing batch jobs comes with some specific challenges, mostly due to the asynchronous nature of how jobs are executed.

In this tutorial, we're going to explore the various alternatives for testing a Spring Batch job.

2. Required Dependencies

We're using spring-boot-starter-batch, so first let's set up the required dependencies in our pom.xml:

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-batch</artifactId>
    <version>2.1.9.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-test</artifactId>
    <version>2.1.9.RELEASE</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.springframework.batch</groupId>
    <artifactId>spring-batch-test</artifactId>
    <version>4.2.0.RELEASE</version>
    <scope>test</scope>
</dependency>

We included the spring-boot-starter-test and spring-batch-test which bring in some necessary helper methods, listeners and runners for testing Spring Batch applications.

3. Defining the Spring Batch Job

Let's create a simple application to show how Spring Batch solves some of the testing challenges.

Our application uses a two-step Job that reads a CSV input file with structured book information and outputs books and book details.

3.1. Defining the Job Steps

The two subsequent Steps extract specific information from BookRecords and then map these to Books (step1) and BookDetails (step2):

@Bean
public Step step1(
  ItemReader<BookRecord> csvItemReader, ItemWriter<Book> jsonItemWriter) throws IOException {
    return stepBuilderFactory
      .get("step1")
      .<BookRecord, Book> chunk(3)
      .reader(csvItemReader)
      .processor(bookItemProcessor())
      .writer(jsonItemWriter)
      .build();
}

@Bean
public Step step2(
  ItemReader<BookRecord> csvItemReader, ItemWriter<BookDetails> listItemWriter) {
    return stepBuilderFactory
      .get("step2")
      .<BookRecord, BookDetails> chunk(3)
      .reader(csvItemReader)
      .processor(bookDetailsItemProcessor())
      .writer(listItemWriter)
      .build();
}

3.2. Defining the Input Reader and Output Writer

Let's now configure the CSV file input reader using a FlatFileItemReader to de-serialize the structured book information into BookRecord objects:

private static final String[] TOKENS = { 
  "bookname", "bookauthor", "bookformat", "isbn", "publishyear" };

@Bean
@StepScope
public FlatFileItemReader<BookRecord> csvItemReader(
  @Value("#{jobParameters['file.input']}") String input) {
    FlatFileItemReaderBuilder<BookRecord> builder = new FlatFileItemReaderBuilder<>();
    FieldSetMapper<BookRecord> bookRecordFieldSetMapper = new BookRecordFieldSetMapper();
    return builder
      .name("bookRecordItemReader")
      .resource(new FileSystemResource(input))
      .delimited()
      .names(TOKENS)
      .fieldSetMapper(bookRecordFieldSetMapper)
      .build();
}

There are a couple of important things in this definition, which will have implications on the way we test.

First of all, we annotated the FlatItemReader bean with @StepScope, and as a result, this object will share its lifetime with StepExecution.

This also allows us to inject dynamic values at runtime so that we can pass our input file from the JobParameters in line 4. In contrast, the tokens used for the BookRecordFieldSetMapper are configured at compile-time.

We then similarly define the JsonFileItemWriter output writer:

@Bean
@StepScope
public JsonFileItemWriter<Book> jsonItemWriter(
  @Value("#{jobParameters['file.output']}") String output) throws IOException {
    JsonFileItemWriterBuilder<Book> builder = new JsonFileItemWriterBuilder<>();
    JacksonJsonObjectMarshaller<Book> marshaller = new JacksonJsonObjectMarshaller<>();
    return builder
      .name("bookItemWriter")
      .jsonObjectMarshaller(marshaller)
      .resource(new FileSystemResource(output))
      .build();
}

For the second Step, we use a Spring Batch-provided ListItemWriter that just dumps stuff to an in-memory list.

3.3. Defining the Custom JobLauncher

Next, let's disable the default Job launching configuration of Spring Boot Batch by setting spring.batch.job.enabled=false in our application.properties.

We configure our own JobLauncher to pass a custom JobParameters instance when launching the Job:

@SpringBootApplication
public class SpringBatchApplication implements CommandLineRunner {

    // autowired jobLauncher and transformBooksRecordsJob

    @Value("${file.input}")
    private String input;

    @Value("${file.output}")
    private String output;

    @Override
    public void run(String... args) throws Exception {
        JobParametersBuilder paramsBuilder = new JobParametersBuilder();
        paramsBuilder.addString("file.input", input);
        paramsBuilder.addString("file.output", output);
        jobLauncher.run(transformBooksRecordsJob, paramsBuilder.toJobParameters());
   }

   // other methods (main etc.)
}

4. Testing the Spring Batch Job

The spring-batch-test dependency provides a set of useful helper methods and listeners that can be used to configure the Spring Batch context during testing.

Let's create a basic structure for our test:

@RunWith(SpringRunner.class)
@SpringBatchTest
@EnableAutoConfiguration
@ContextConfiguration(classes = { SpringBatchConfiguration.class })
@TestExecutionListeners({ DependencyInjectionTestExecutionListener.class, 
  DirtiesContextTestExecutionListener.class})
@DirtiesContext(classMode = ClassMode.AFTER_CLASS)
public class SpringBatchIntegrationTest {

    // other test constants
 
    @Autowired
    private JobLauncherTestUtils jobLauncherTestUtils;
  
    @Autowired
    private JobRepositoryTestUtils jobRepositoryTestUtils;
  
    @After
    public void cleanUp() {
        jobRepositoryTestUtils.removeJobExecutions();
    }

    private JobParameters defaultJobParameters() {
        JobParametersBuilder paramsBuilder = new JobParametersBuilder();
        paramsBuilder.addString("file.input", TEST_INPUT);
        paramsBuilder.addString("file.output", TEST_OUTPUT);
        return paramsBuilder.toJobParameters();
   }

The @SpringBatchTest annotation provides the JobLauncherTestUtils and JobRepositoryTestUtils helper classes. We use them to trigger the Job and Steps in our tests.

Our application uses Spring Boot auto-configuration, which enables a default in-memory JobRepository. As a result, running multiple tests in the same class requires a cleanup step after each test run.

Finally, if we want to run multiple tests from several test classes, we need to mark our context as dirty. This is required to avoid the clashing of several JobRepository instances using the same data source.

4.1. Testing the End-To-End Job

The first thing we'll test is a complete end-to-end Job with a small data-set input.

We can then compare the results with an expected test output:

@Test
public void givenReferenceOutput_whenJobExecuted_thenSuccess() throws Exception {
    // given
    FileSystemResource expectedResult = new FileSystemResource(EXPECTED_OUTPUT);
    FileSystemResource actualResult = new FileSystemResource(TEST_OUTPUT);

    // when
    JobExecution jobExecution = jobLauncherTestUtils.launchJob(defaultJobParameters());
    JobInstance actualJobInstance = jobExecution.getJobInstance();
    ExitStatus actualJobExitStatus = jobExecution.getExitStatus();
  
    // then
    assertThat(actualJobInstance.getJobName(), is("transformBooksRecords"));
    assertThat(actualJobExitStatus.getExitCode(), is("COMPLETED"));
    AssertFile.assertFileEquals(expectedResult, actualResult);
}

Spring Batch Test provides a useful file comparison method for verifying outputs using the AssertFile class.

4.2. Testing Individual Steps

Sometimes it's quite expensive to test the complete Job end-to-end and so it makes sense to test individual Steps instead:

@Test
public void givenReferenceOutput_whenStep1Executed_thenSuccess() throws Exception {
    // given
    FileSystemResource expectedResult = new FileSystemResource(EXPECTED_OUTPUT);
    FileSystemResource actualResult = new FileSystemResource(TEST_OUTPUT);

    // when
    JobExecution jobExecution = jobLauncherTestUtils.launchStep(
      "step1", defaultJobParameters()); 
    Collection actualStepExecutions = jobExecution.getStepExecutions();
    ExitStatus actualJobExitStatus = jobExecution.getExitStatus();

    // then
    assertThat(actualStepExecutions.size(), is(1));
    assertThat(actualJobExitStatus.getExitCode(), is("COMPLETED"));
    AssertFile.assertFileEquals(expectedResult, actualResult);
}

@Test
public void whenStep2Executed_thenSuccess() {
    // when
    JobExecution jobExecution = jobLauncherTestUtils.launchStep(
      "step2", defaultJobParameters());
    Collection actualStepExecutions = jobExecution.getStepExecutions();
    ExitStatus actualExitStatus = jobExecution.getExitStatus();

    // then
    assertThat(actualStepExecutions.size(), is(1));
    assertThat(actualExitStatus.getExitCode(), is("COMPLETED"));
    actualStepExecutions.forEach(stepExecution -> {
        assertThat(stepExecution.getWriteCount(), is(8));
    });
}

Notice that we use the launchStep method to trigger specific steps.

Remember that we also designed our ItemReader and ItemWriter to use dynamic values at runtime, which means we can pass our I/O parameters to the JobExecution (lines 9 and 23).

For the first Step test, we compare the actual output with an expected output.

On the other hand, in the second test, we verify the StepExecution for the expected written items.

4.3. Testing Step-scoped Components

Let's now test the FlatFileItemReader. Recall that we exposed it as @StepScope bean, so we'll want to use Spring Batch's dedicated support for this:

// previously autowired itemReader

@Test
public void givenMockedStep_whenReaderCalled_thenSuccess() throws Exception {
    // given
    StepExecution stepExecution = MetaDataInstanceFactory
      .createStepExecution(defaultJobParameters());

    // when
    StepScopeTestUtils.doInStepScope(stepExecution, () -> {
        BookRecord bookRecord;
        itemReader.open(stepExecution.getExecutionContext());
        while ((bookRecord = itemReader.read()) != null) {

            // then
            assertThat(bookRecord.getBookName(), is("Foundation"));
            assertThat(bookRecord.getBookAuthor(), is("Asimov I."));
            assertThat(bookRecord.getBookISBN(), is("ISBN 12839"));
            assertThat(bookRecord.getBookFormat(), is("hardcover"));
            assertThat(bookRecord.getPublishingYear(), is("2018"));
        }
        itemReader.close();
        return null;
    });
}

The MetadataInstanceFactory creates a custom StepExecution that is needed to inject our Step-scoped ItemReader.

Because of this, we can check the behavior of the reader with the help of the doInTestScope method.

Next, let's test the JsonFileItemWriter and verify its output:

@Test
public void givenMockedStep_whenWriterCalled_thenSuccess() throws Exception {
    // given
    FileSystemResource expectedResult = new FileSystemResource(EXPECTED_OUTPUT_ONE);
    FileSystemResource actualResult = new FileSystemResource(TEST_OUTPUT);
    Book demoBook = new Book();
    demoBook.setAuthor("Grisham J.");
    demoBook.setName("The Firm");
    StepExecution stepExecution = MetaDataInstanceFactory
      .createStepExecution(defaultJobParameters());

    // when
    StepScopeTestUtils.doInStepScope(stepExecution, () -> {
        jsonItemWriter.open(stepExecution.getExecutionContext());
        jsonItemWriter.write(Arrays.asList(demoBook));
        jsonItemWriter.close();
        return null;
    });

    // then
    AssertFile.assertFileEquals(expectedResult, actualResult);
}

Unlike the previous tests, we are now in full control of our test objects. As a result, we're responsible for opening and closing the I/O streams.

5. Conclusion

In this tutorial, we've explored the various approaches of testing a Spring Batch job.

End-to-end testing verifies the complete execution of the job. Testing individual steps may help in complex scenarios.

Finally, when it comes to Step-scoped components, we can use a bunch of helper methods provided by spring-batch-test. They will assist us in stubbing and mocking Spring Batch domain objects.

As usual, we can explore the complete codebase over on GitHub.

Spring bottom

I just announced the new Learn Spring course, focused on the fundamentals of Spring 5 and Spring Boot 2:

>> CHECK OUT THE COURSE

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