How to make "negative" unit tests?

[alessandro-gomma]

In our streams we would like to create some unit tests to verify that when the stream process a broken message, the stream handles the error correctly (logging, eventual post-processing, etc..).

If we write a unit test with a broken message as input, the stream correctly handles the error but the test fails with the "wrong batch count, expected 1, got 0" message.

Is there any way to test this?

Sample configuration as reference:

input:
  broker:
    inputs:
      <<< input >>>
pipeline:
  processors:
    - mapping: |
      <<< map & process>>>
    - catch:
        - log:
            level: ERROR
            message: "Processing failed due to: ${!error()} | message ${!content()}"
        - mapping: root = if errored() { deleted() }
output:
  <<< output >>>

Thanks!

[mihaitodor]

Hey @alessandro-gomma 👋 One approach is to write a test which expects 0 batches:

pipeline:
  processors:
    - mapping: |
        root = throw("kaboom!")
    - catch:
        - mapping: root = if errored() { deleted() }

tests:
  - name: test deleted
    target_processors: '/pipeline/processors'
    input_batch:
      - content: 'foobar'
    output_batches: []

Alternatively, depending on what your pipeline does and where you place that mapping processor which contains the deleted() call, you could mock it such that it returns some dummy data instead. Something like this:

pipeline:
  processors:
    - mapping: |
        root = throw("kaboom!")
    - catch:
        - label: mockme
          mapping: root = if errored() { deleted() }


tests:
  - name: test deleted
    target_processors: '/pipeline/processors'
    mocks:
      mockme:
        mapping: root = "ERROR"
    input_batch:
      - content: 'foobar'
    output_batches:
      -
        - content_equals: ERROR