莫基托 | JUnit | Avro：模拟 void 方法不起作用

Question

I wrote a method for avro serialization, which I want to test.

Method

@SneakyThrows
@Override
public byte[] serialize(String topic, T data) {
    try (ByteArrayOutputStream stream = new ByteArrayOutputStream()) {
        writeSerializedAvro(stream, data, data.getSchema());
        return stream.toByteArray();
    } catch (IOException e) {
        throw new AvroSerializationException(e.getMessage(), e);
    }
}

private void writeSerializedAvro(ByteArrayOutputStream stream, T data, Schema schema) throws IOException {
    binaryEncoder = EncoderFactory.get().binaryEncoder(stream, binaryEncoder);
    DatumWriter<T> datumWriter = new GenericDatumWriter<>(schema);
    datumWriter.write(data, binaryEncoder);
    binaryEncoder.flush();
}

datumWriter.write or binaryEncoder.flush() can throw IOException .

In the test, I want to see if IOException is thrown, my method catchers it and wraps it in AvroSerializationException (a class written by me).

Unit Test

    @Test(expected = AvroSerializationException.class)
public void testSerializeException() throws IOException {
    // Given 
// need to mock here

    // When
    serializer.serialize("", avroObject);
}

I have tried mocking GenericDatumWriter , BufferedBinaryEncoder and EncoderFactory with doThrow().when() methods but nothing worked for me.

BufferedBinaryEncoder binaryEncoder = Mockito.mock(BufferedBinaryEncoder.class);
Mockito.doThrow(new IOException()).when(binaryEncoder).flush();

And

    GenericDatumWriter datumWriter = Mockito.mock(GenericDatumWriter.class);
    Mockito.doThrow(new IOException()).when(datumWriter).write(any(), any());

But again, the question comes back to, how am I supposed to pass these objects to my serializer, keeping the best practices in mind?

Answer 1

You need first to mock the object using Mockito and use it in your class and then the exception will be thrown, like below:

Your code:

private DatumWriter<T> datumWriter = new GenericDatumWriter<>(schema);

@SneakyThrows
@Override
public byte[] serialize(String topic, T data) {
    try (ByteArrayOutputStream stream = new ByteArrayOutputStream()) {
        writeSerializedAvro(stream, data, data.getSchema());
        return stream.toByteArray();
    } catch (IOException e) {
        throw new AvroSerializationException(e.getMessage(), e);
    }
}

private void writeSerializedAvro(ByteArrayOutputStream stream, T data, Schema schema) throws IOException {
    binaryEncoder = EncoderFactory.get().binaryEncoder(stream, binaryEncoder);
    datumWriter.write(data, binaryEncoder);
    binaryEncoder.flush();
}

public void setDatumWriter (DatumWriter datumWriter){
   this.datumWriter=datumWriter;
}

Your test code:

@Test(expected = AvroSerializationException.class)
public void testSerializeException() throws IOException {
    // Given 
    DatumWriter<YourClass> datumWriter = Mockito.mock(DatumWriter<YourClass>.class);
    when(datumWriter.write(anyObject(), anyObject())).thenThrow(IOException.class);
    
    serializer.setDatumWriter(datumWriter);  
   
    serializer.serialize("", avroObject);
}