Testing microservices
=====================
Imagine you have a Metrics for IOT, with microservice architecture::

                                     Metrics And Events
    Metrics ---> Receiver ---> Kafka --------> Saver ------> Postres
                                || /\                           ||
                       Metrics  || ||                           || Metrics
                                || || Events                    || and Events
                                \/ ||                           \/
                                Processor <-------> Redis      Assessor -------------> Events
                                           Warning                      -------------> Sensor Statistics
                                           counters

| `Metrics` service collect metrics from devices and sends to the `Receiver`.
| `Receiver` aggregates metrics and sends them to `Kafka`.
| `Processor` reads metrics from `Kafka`, process them and puts generated events back to `Kafka`.
  It also uses `Redis` for warning counters storage.
| `Saver` microservice saves all metrics and generated events to `Postgres`.
| Finally `Assessor` takes events and statistics from `Postgres` and renders it to user or external services.

How to test?
------------
| Each input request pass through the 9 services. Error can be in any of them. And full coverage of one service with unit
  or functional tests won't help you, because bug can be everywhere. In deploy configuration, wrong protocol in microservices
  communication, etc...

Catcher will help you::

    ---
    include:
        - file: metrics_check.yaml
          as: metrics_check
    variables:
      metric1: '{{ RANDOM_INT }}'
      device_id: '{{ RANDOM_STR }}'
      metric2: 5000 # this value will generate warning
    steps:
        - http: # send data to the Metrics service
            actions:
              - post:
                  url: '{{ metrics_url }}/metric'
                  body: {device_id: '{{ device_id }}', value: '{{ metric1 }}'}
              - post:
                  url: '{{ metrics_url }}/metric'
                  body: {device_id: '{{ device_id }}', value: '{{ metric2 }}'}
        - kafka: # check Receiver put aggregate metric in kafka
            consume:
                server: '{{ kafka }}'
                topic: 'metrics'
                where:
                    equals: {the: '{{ MESSAGE.device_id }}', is: '{{ device_id }}'}
            register: {value: '{{ OUTPUT.value }}'}
        - check: # check metric's value was properly aggregated
             equals: {the: '{{ value }}', is: '{{ metric1 + metric2 }}'}
        - wait: {seconds: 0.5}
        - kafka: # check event for metric2 was generated
            consume:
                server: '{{ kafka }}'
                topic: 'events'
                where:
                    and:
                      - equals: {the: '{{ MESSAGE.device_id }}', is: '{{ device_id }}'}
                      - equals: {the: '{{ MESSAGE.value }}', is: '{{ metric2 }}'}
        - postgres:  # check Saver put 2 metrics in Postgres
            sql: 'select value from metrics where device_id == {{ device_id }}'
            register: {metrics: '{{ OUTPUT.value }}'}
        - run: metrics_check
        - postgres:  # check Saver put event in Postgres
            sql:  'select count(*) from events where device_id = {{ device_id }} and value = {{ metric2 }}'
            register: {event: '{{ OUTPUT.count }}'}
        - check: '{{ event == 1 }}'
        - http:  # request statistics from Assessor
            actions:
              - get:
                  url: '{{ assessor_url }}/statistics?device_id={{ device_id }}'
                register: {measurements: '{{ OUTPUT.measurements }}'}
              - get:
                  url: '{{ assessor_url }}/events?device_id={{ device_id }}'
                register: {events: '{{ OUTPUT.events }}'}
        - run: # check proper statistics
            include: metrics_check
            variables: {metrics: '{{ measurements }}'}
        - check:
            contains: {the: '{{ metric2 }}', in: '{{ events }}'}

`metrics_check.yaml`::

    ---
    steps:
        - check:
            and:
              - equals: '{{ metrics|length == 2 }}'
              - contains: {the: '{{ metric1 }}', in: '{{ metrics }}'}
              - contains: {the: '{{ metric2 }}', in: '{{ metrics }}'}

With this Catcher test scenario you can always be sure, that every component of your system is working properly.