如何测试创建目录和文件系统的方法

Question

This is my method, which creates a file system when gets called.

/**
     * Process all messages from {@code messagesDir} directory and save results in {@code resultsDir}
     *
     * @param messagesDir      messages directory
     * @param resultsDir       results directory
     * @param logDirectory     directory where should be written logs
     * @param cleanupResultDir whether cleanup result directory
     * @throws PtfProcessorException if provided {@code messagesDir} is invalid directory or there was comparision exception
     */
    public void processMessages(String messagesDir, String resultsDir, String logDirectory, boolean cleanupResultDir)
            throws PtfProcessorException {
        // check if the directories are valid
        checkIsValidDirectory(messagesDir);
        checkIsValidDirectory(resultsDir);

        // get operations directories
        final File[] operationsDirsFiles = getInnerDirs(messagesDir);

        // get results directory and clean up it if cleanupResultDirectory is true
        final File resultsDirFile = new File(resultsDir);
        if (cleanupResultDir) {
            cleanUpDirectory(resultsDirFile);
        }

        // compare messages by operation bases
        for (File operationDirFile : operationsDirsFiles) {
            // operation log directory file
            final File logOperationDirFile = new File(logDirectory, operationDirFile.getName());
            try {
                compareOperationMessages(operationDirFile, resultsDirFile, logOperationDirFile);
            } catch (PtfProcessorException e) {
                writeExceptionLog("Exception while comparing operation: " + operationDirFile.getName(),
                        e, logOperationDirFile);
            }
        }
    }

Now I must write a unit test for this method. I have read several posts related to "TemporaryFolder" in Mockito and "Rule" annotation, but to tell the the truth, I do not know which approach I need. Anybody please help me to find a way for testing this method. If there is a necessity for providing the helper methods used in aforementioned method, I can provide them.

Answer 1

One of the aproaches may be to create wrapper class for File and then provide it into the class that this method resides. Then you will be able to mock it with mockito and verify whether proper methods were invoked.

Normally you should not test classes that are not in your project, ( File for example). This is not a good practice while writing unit tests. The thing that you can test is behavior of your method, that is whether proper external methods were invoked.

You should also remember to check if the validation is working by providing various inputs in your unit tests.

Answer 2

I suggest to use JUnit's TemporaryFolder rule.

public class YourTest {
  @Rule
  public final TemporaryFolder folder = new TemporaryFolder();

  @Test
  public void verifySomeFileBehaviour() throws Exception {
    File messagesDir = folder.newFolder();
    File reportsDir = folder.newFolder();
    File logsDir = folder.newFolder();

    //create your object and then
    yourObject.processMessages(
      messagesDir.getAbsolutePath(),
      reportsDir.getAbsolutePath(),
      logsDir.getAbsolutePath(),
      true
    );

    //now you can verify the contents. E.g.
    assertTrue( new File( messagesDir, "firstMessage.txt" ).exists() );
  }
}

I recommend to use AssertJ as assertion library because it has nice assertions for files.

Answer 3

The real issue here: you created hard to test code - because you are implementing more than one responsibility in this method. Instead of collecting file names, and then creating them, your method could for example look like this:

public void processMessages(String messagesDir, String resultsDir, String logDirectory, boolean cleanupResultDir)
        throws PtfProcessorException {
    directoryValidator.validate(messagesDir, resultsDir);

    final File[] operationsDirsFiles = getInnerDirs(messagesDir);

    cleanupService.cleanup(cleanupResultDir, resultsDirFile);
    fileService.create(operationsDirsFiles)

The above is merely meant as "pseudo code" to give you some ideas. The core point is: by extracting behavior into its own class/interface you enable yourself to test each functionality separately. And later on, you can use dependency injection to make that functionality available to more complex methods. You see - you could now mock all those "service" objects; and all of a sudden you only talk about verifying that you pass a certain list of File objects to another method.

Long story short: as usual the answer is: write testable code. Follow clean code rules, such as single responsibility principle . And when you do that, the quality of your production code will improve; and your tests will be much simpler to write down. Without the need to do fake file system operation all over the place.