# Unit Testing

Just as with other application styles, it is extremely important to unit test any code written as part of a batch job as well. The Spring core documentation covers how to unit and integration test with Spring in great detail, so it won't be repeated here. It is important, however, to think about how to 'end to end' test a batch job, which is what this chapter will focus on. The spring-batch-test project includes classes that will help facilitate this end-to-end test approach.

## Creating a Unit Test Class

In order for the unit test to run a batch job, the framework must load the job's ApplicationContext. Two annotations are used to trigger this:

- `@RunWith(SpringJUnit4ClassRunner.class)`: Indicates that the class should use Spring's JUnit facilities

- `@ContextConfiguration(locations = {...})`: Indicates which XML files contain the ApplicationContext.

      @RunWith(SpringJUnit4ClassRunner.class)
      @ContextConfiguration(locations = { "/simple-job-launcher-context.xml", "/jobs/skipSampleJob.xml" })
      public class SkipSampleFunctionalTests extends AbstractJobTests { ... }

## End To End Testing Batch Jobs

'End To End' testing can be defined as testing the complete run of a batch job from beginning to end. This allows for a test that sets up a test condition, executes the job, and verifies the end result.

In the example below, the batch job reads from the database and writes to a flat file. The test method begins by setting up the database with test data. It clears the CUSTOMER table and then inserts 10 new records. The test then launches the `Job` using the `launchJob()` method. The `launchJob`() method is provided by the `AbstractJobTests` parent class. Also provided by the super class is `launchJob(JobParameters)`, which allows the test to give particular parameters. The `launchJob()` method returns the `JobExecution` object which is useful for asserting particular information about the `Job` run. In the case below, the test verifies that the `Job` ended with status "COMPLETED".

      @RunWith(SpringJUnit4ClassRunner.class)
      @ContextConfiguration(locations = { "/simple-job-launcher-context.xml", "/jobs/skipSampleJob.xml" })
      public class SkipSampleFunctionalTests extends AbstractJobTests {

          private SimpleJdbcTemplate simpleJdbcTemplate;

          @Autowired
          public void setDataSource(DataSource dataSource) {
              this.simpleJdbcTemplate = new SimpleJdbcTemplate(dataSource);
          }

          @Transactional
          @Test
          public void testJob() throws Exception {
              simpleJdbcTemplate.update("delete from CUSTOMER");
              for (int i = 1; i <= 10; i++) {
                  simpleJdbcTemplate.update("insert into CUSTOMER values (?, 0, ?, 100000)", i, "customer" + i);
              }

              JobExecution jobExecution = this.launchJob();

              Assert.assertEquals("COMPLETED", jobExecution.getExitStatus());
          }
      }

## Testing Individual Steps

For complex batch jobs, test cases in the end-to-end testing approach may become unmanageable. It these cases, it may be more useful to have test cases to test individual steps on their own. The `AbstractJobTests` class contains a method `launchStep` that takes a step name and runs just that particular `Step`. This approach allows for more targeted tests by allowing the test to set up data for just that step and to validate its results directly.

      JobExecution jobExecution = this.launchStep("loadFileStep");

## Validating Output Files

When a batch job writes to the database, it is easy to query the database to verify that the output is as expected. However, if the batch job writes to a file, it is equally important that the output be verified. Spring Batch provides a class `AssertFile` to facilitate the verification of output files. The method `assertFileEquals` takes two `File` objects (or two `Resource` objects) and asserts, line by line, that the two files have the same content. Therefore, it is possible to create a file with the expected output and to compare it to the actual result:

      private static final String EXPECTED_FILE = "src/main/resources/data/iosample/input/multiLine.txt";
      private static final String OUTPUT_FILE = "target/test-outputs/multiLineOutput.txt";

      AssertFile.assertFileEquals(new FileSystemResource(EXPECTED_FILE), new FileSystemResource(OUTPUT_FILE));

## Mocking Domain Objects

Another common issue encountered while writing unit and integration tests for Spring Batch components is how to mock domain objects. A good example is a `StepExecutionListener`, as illustrated below:

      public class NoWorkFoundStepExecutionListener extends StepExecutionListenerSupport {

        public ExitStatus afterStep(StepExecution stepExecution) {
          if (stepExecution.getReadCount() == 0) {
            throw new NoWorkFoundException("Step has not processed any items");
          }
          return stepExecution.getExitStatus();
        }
      }

The above listener is provided by the framework and checks a `StepExecution` for an empty read count, thus signifying that no work was done. While this example is fairly simple, it serves to illustrate the types of problems that may be encountered when attempting to unit test classes that implement interfaces requiring Spring Batch domain objects. Consider the above listener's unit test:

        private NoWorkFoundStepExecutionListener tested = new NoWorkFoundStepExecutionListener();

        @Test
        public void testAfterStep() {
            StepExecution stepExecution = new StepExecution("NoProcessingStep",
                    new JobExecution(
                    new JobInstance(1L, new JobParameters(), "NoProcessingJob")));

            stepExecution.setReadCount(0);

            try {
                tested.afterStep(stepExecution);
                fail();
            } catch (NoWorkFoundException e) {
               assertEquals("Step has not processed any items", e.getMessage());
            }
        }

Because the Spring Batch domain model follows good object orientated principles, the StepExecution requires a `JobExecution`, which requires a `JobInstance` and `JobParameters` in order to create a valid `StepExecution`. While this is good in a solid domain model, it does make creating stub objects for unit testing verbose. To address this issue, the Spring Batch test module includes a factory for creating domain objects: `MetaDataInstanceFactory`. Given this factory, the unit test can be updated to be more concise:

        private NoWorkFoundStepExecutionListener tested = new NoWorkFoundStepExecutionListener();

        @Test
        public void testAfterStep() {
            StepExecution stepExecution = MetaDataInstanceFactory.createStepExecution();

            stepExecution.setReadCount(0);

            try {
                tested.afterStep(stepExecution);
                fail();
            } catch (NoWorkFoundException e) {
               assertEquals("Step has not processed any items", e.getMessage());
            }
        }

The above method for creating a simple `StepExecution` is just one convenience method available within the factory. A full method listing can be found in its Javadoc.