Reusable "mock" task/step

[elliotgunton]

Is your feature request related to a problem? Please describe.
When writing workflows, especially complicated DAGs, it would be useful to mock out Tasks when running the actual workflow, with predefined outputs/status.

Describe the solution you'd like
Reusable MockTask/MockStep (names TBD) that let me specify the inputs it accepts (maybe validating them?) and the outputs it should set. Then users can construct workflows that test specific parts of the DAG, and also skip expensive compute steps. They can even mock the whole Workflow to get an idea of execution paths through the DAG.

We should be able to replace particular DAGs/Steps in an existing Workflow.

Describe alternatives you've considered

• Running expensive Workflows anyway.
• Create our own mock task/step constructors

Additional context
Add any other context or screenshots about the feature request here.

[Reggelord]

Came across this today. If no one else is working on it and it's suitable as a first contribution for a newcomer, I'd be happy to pick it up.

[elliotgunton]

Hi @Reggelord, thanks for your interest! 🙌🏻 Right now this issue isn't suitable for a first time contribution as we need more concrete criteria and code examples for this feature - we're not too sure right now how much effort it will take to include features like mocked outputs.

We'll need to prioritise feature enhancements in the next maintainers meeting, in the mean time please join us on the CNCF slack!