Implementation of topics channel testing for processes and workflows

[nvnieuwk]

This PR implements the long awaited support for topic channels in process and workflow tests.

Currently this PR is not complete, I will update the following list whenever some new steps are done, but feel free to test this branch out already!

• Implement topic channels testing for processes
• Implement topic channels testing for workflows
• Add tests for this feature
• Update the documentation

You can test the topic channels in the following way:

nextflow_process {
    name "Test Process TEST"
    script "main.nf"
    process "TEST"

    topics 'test', 'other' // Define topics to be checked for for all tests in this test file
    test("Should run without failures") {

        topics 'another' // Define topics to be checked for in this test only (this expands the topics defined in the upper scope)

        when {
            process {
                """
                input[0] = "test"
                """
            }
        }
        then {
            assert process.success
            assert snapshot(topics).match() // the 'topics' property functions the same as the 'process.out' property, meaning that you can access the specific topics using 'topic.<key>' or 'topic.get("<key>")' or 'topic["<key>"]'
        }
    }
}

Any feedback would be greatly appreciated! If you need a compiled jar file of this branch, feel free to ask me :)

[nvnieuwk]

An example snapshot from topics looks like this:

{
    "Should run without failures": {
        "content": [
            {
                "another": [
                    
                ],
                "other": [
                    
                ],
                "test": [
                    "test.txt:md5,e4439267203fb5277d347e6cd6e440b5"
                ]
            }
        ],
        "timestamp": "2026-03-13T15:49:49.276661043",
        "meta": {
            "nf-test": "0.9.4",
            "nextflow": "25.10.4"
        }
    }
}

This is for a process that has one output topic called test

[maxulysse]

LGTM

[lukfor]

Great work! 👍👌