Demonstrate migration path from JUnit 4 to JUnit 5

[sbrannen]

Overview

Based on discussions I've had with developers in the community, it is apparent that some people fear an upgrade from JUnit 4 to JUnit 5. Aside from the fact that it's totally feasible to run JUnit 4 tests alongside JUnit 5 tests, we should still attempt to migrate an existing JUnit 4 test suite just to see where the hurdles are.

Proposal

Demonstrate how to migrate from JUnit 4's ExpectedException Rule to a JUnit 5 Extension-based alternative.

Food for Thought

Can this be achieved with simple search-and-replace?

Can a JUnit 5 extension be implemented that honors JUnit 4's ExpectedException transparently, without the need to modify a single line within test methods -- for example, by removing @Rule from the ExpectedException field and adding @ExtendWith(SomeExpectedExceptionExtension.class)?

Related Issues

• Document compatibility with JUnit 4 TestRules #343

Related Blogs

• How to Replace Rules in JUnit 5

[philwebb]

The other one I use quite often is TemporaryFolder

[sormuras]

@philwebb Me, too! See junit-team/junit-examples#4

[kcooney]

The lack of Rule support in JUnit5 might make it hard for large projects to incrementally migrate test classes, especially if they have custom Rules.

I wonder if we could have an optional jar that defines a simple extension point that can be used for JUnit5 and JUnit4. I find that most of our Rules only need the following:

• setUp()
• tearDown() - called only if setUp() called
• verify() - called only if the test method doesn't throw

If this interests anyone, I could write up a proposal.

[akozlova]

Hi Kevin,

I thought about IDE-side migration tool to ease the transition. Of cause it
doesn't make the jar useless.

BTW If you have 'rules' for such tool in mind, it would help me a lot.

Thanks,
Anna

On Fri, Mar 25, 2016 at 4:47 PM, Kevin Cooney notifications@github.com
wrote:

The lack of Rule support in JUnit5 might make it hard for large projects
to incrementally migrate test classes, especially if they have custom Rules.

I wonder if we could have an optional jar that defines a simple extension
point that can be used for JUnit5 and JUnit4. I find that most of our Rules
only need the following:

• setUp()
• tearDown() - called only if setUp () called
• verify() - called only if the test method doesn't throw

If this interests anyone, I could write up a proposal.

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[marcphilipp]

@kcooney: Can you please elaborate your proposal a bit more?

[sbrannen]

Related blog post:

http://www.codeaffine.com/2016/04/06/replace-rules-in-junit5/