Mocking Operations

[richardboehme]

In some cases one might prefer to mock Operation calls. This might be helpful, when testing Operations that invoke Subprocesses that are not of interest in the test.

One example of doing this can be seen here (using the mocha gem):

signal = Song::Operation::Create.to_h[:outputs].find { |output| output.signal.to_h[:semantic] == :success }.signal
Song::Operation::Create.expects(:call).once.with do |(ctx, _)|
  !ctx[:name].empty? &&
    ctx[:length].to_i > 0
end.returns([signal, Trailblazer::Context({ song: Song.new })])

I believe we could benefit from providing a universial way of defining such expectations. The current way of doing this is kinda complicated:

• You have to extract the correct signal instance from the operation yourself.
• There are different call interfaces (when using in Subprocess vs. calling the operations yourself)
• If you want to mock a Subprocess you have to know the circuit interface

It may be possible to provide a simpler interface which allows:

• return different signals (by name/class?)
• expect specific inputs
• return a specific new context (which might depend on the inputs?) => define outputs