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What is the way to do in Java unit testing what one does by Patch and MagicMock in Python unit tests

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posted 7 months ago

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In python unit testing, unit tests are written with help of Patch and MagicMock . Reference: https://docs.python.org/3/library/unittest.mock.html What is the way in Java unit tests to do what is dong using Patch and to do what is done using Magic Mock of python? Thanks

Tim Holloway

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posted 7 months ago

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There are several different Unit Testing and Mocking platforms for Java.

JUnit is popular for unit testing. In a Maven project, you'd put the test classes under the project's /src/test/java directory so that they would not be included in production builds.

Mockito is one of several Mock frameworks in common use.

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Monica Shiralkar

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Tim Holloway wrote:

Mockito is one of several Mock frameworks in common use.

Yes, in Mockito, what I am trying to understand is that what is the way to do the part that we can do using patch in Python unit tests and what is the way to do the part that one can do using MagicMock in Python unit tests (does Mock() of Java do the same or anything else)?

Tim Holloway

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Somewhere on the Ranch, I believe I published about 6 "gotchas" for mocking in Java. I wish I could remember where.

But the #1 rule was never mock if you had a better alternative.

Mockito's mocking doesn't simulate the mocked objects as much as it simply makes a "black hole" for the rest of the code to plug into. Unless you go to a lot of effort, the mocked methods do nothing and return nothing, null, or zero. And it's even worst if you need to mock something stateful.

In Java, a better approach is to define an Interface and a simulated implementation of that Interface, then wire it in in place of the production implementation, This works especially well when using a wiring framework such as Spring.

You cannot always do that, of course, and sometimes you do need something like Mockito, but again, it's a last resort for me.

Liutauras Vilda

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posted 7 months ago

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Monica Shiralkar wrote:
Yes, in Mockito, what I am trying to understand is that what is the way to do the part that we can do using patch in Python unit tests and what is the way to do the part that one can do using MagicMock in Python unit tests (does Mock() of Java do the same or anything else)?

It is hard to answer to this question, unless you know exactly how both frameworks work, what are their similarities and differences.

You better tell, what do you want to do with Java in your unit tests, and then we might help you how to achieve that.

But briefly looking at those you mentioned for Python, I think Mockito does all that, or at least to most extent.

Rob Spoor

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I'm not really familiar with Python's patch options, but perhaps Mockito's equivalent is a spy. You take a normal object, and Mockito wraps it for you. Unless you tell Mockito to replace method calls it will call the actual methods. And a bonus is that you can verify that calls were made afterwards - even for non-mocked methods.

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Monica Shiralkar

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Thanks. I will read on spy in Mockito.

Tim Holloway

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Fair warning, though. Java 9 changed how introspection works, and that impacted Mockito a lot. Since the Internet is great at serving up stale data, make sure that anything you read is up to date.

The original spy mechanism was also pretty cumbersome but it's much more streamlined now,