In unit test, real code is run instead of function stub & mocked object

Question

It is a very simple unit test case.

I have two methods in class School :

protected S3Object getAwsObject(AmazonS3Client client, String bucketName, String keyName) {
        GetObjectRequest objRequest =  new GetObjectRequest(bucketName, keyName);
        return client.getObject(objRequest);
}

Above method is invoked by the 2nd method showing below:

public void doTask() {
   // get client
   AmazonS3Client client = getAwsS3Client();
   // invoke the 1st method
   S3Object s3Obj = getAwsObject(client, "my-bucket", "my-key");
   ...
}

I use Mockito to test the method doTask() , I tried to mock the AmazonS3Client & stub function getAwsObject() :

@Test
public void testDoTask() {
   // partially mocked School instance
   School school = new School();
   School schoolSpy = Mockito.spy(school);
   // mock the client & s3 object
   AmazonS3Client mockedClient = Mockito.mock(AmazonS3Client.class);

   S3Object mockedS3Obj = Mockito.mock(S3Object.class);

   Mockito.doReturn(mockedClient)
       .when(schoolSpy).getAwsS3Client();

   // PROBLEM HERE: I stub function to return mocked S3Object, but real code is run
   Mockito.doReturn(mockedS3Obj)
          .when(schoolSpy).getAwsObject(mockedClient, "my-bucket", "my-key");

   // system under test
   schoolSpy.doTask();
}

When run the test, I got the following error:

com.amazonaws.services.s3.model.AmazonS3Exception: 
The AWS Access Key Id you provided does not exist in our records. 

(Service: Amazon S3; Status Code: 403; Error Code: InvalidAccessKeyId; Request ID: 6B973FC095C28524),...

Looks like the test case run the real code client.getObject(objRequest) instead of using the stub of getAwsObject(...) , WHY?

Answer 1

If you don't succeed in making your mocking work, you can solve your problem by overriding the original methods this way:

// mock the client & s3 object
final AmazonS3Client mockedClient = Mockito.mock(AmazonS3Client.class);
final S3Object mockedS3Obj = Mockito.mock(S3Object.class);

School school = new School(){

  @Override
  protected S3Object getAwsObject(AmazonS3Client client, String bucketName, String keyName) {
    return mockedS3Obj;
  }

  @Override
  protected AmazonS3Client getAwsS3Client() {
    return mockedClient;
  }

};

// system under test
school.doTask();

Answer 2

First, you should not use spy but in legacy code. ( http://site.mockito.org/mockito/docs/current/org/mockito/Mockito.html#spy%28T%29 ). If you delegate the creation of objects in not static factories/builders it will be easy to test.

But, in this case, if mockito executes the real code, then your doReturn... is not valid. I think that Mockito does not validate the params clause and then it not launchs the doReturn clause.

You have

doReturn...getAwsObject(mockedClient, "my-bucket", "my-key")

If you do the next and it works then i am right 100%

doReturn...getAwsObject(any(AmazonS3Client.class), anyString(), anyString())

I had problems when i used mock params and not-mock params in the same statement. try this:

getAwsObject(mockedClient, eq("my-bucket"), eq("my-key")); 

If this does not work try with another solution like:

eq(mockedClient), eq(...), eq(...)

Finally, if it does not work, maybe @max solution will be easier.

Answer 3

Multiple wrong things are done here.

Spy should not be created for the Class under test.

Unit test are written for whole class to test behaviours in the class. If the methods in the same class are Mocked, then whats the purpose of unit tests?

Only dependent classes should be mocked and possible provide setter methods to set these dependencies. This way it can be decided whether to inject real objects or mocked objects.