[Metricbeat][ Add option to remove fields from comparison in mocked tests and mage target

[sayden]

Added 3 things:

• Config option remove_fields_from_comparison to remove fields from the JSON generated and expected files to byte-to-byte comparison when asserting tests.
• Added a README.md file to the folder where the code is located showing current options, flags and use.
• Added a mage target called mockedTests to avoid navigating to beats/metricbeat/mb/testing/data to run tests.

The PR can be considered a WIP but some overlook might be nice @ruflin to know if you like the current heading and altitude 😉

[sayden]

There's a Package field in GoTestArgs type but the order of the executed contents isn't correct when using it. By placing everything as ExtraFlag I could control the order of the flags and package run.

[ruflin]

Probably @andrewkroh knows best here.

[sayden]

@ruflin I modified this from MarshalIndent to just Marshal. I understood that the idea of using indent was to write into the data.json file in pretty format but for comparison it wasn't nice when it failed as the console was escaping newlines like here

[ruflin]

No strong preference as long as the files written to disk are indented.

For the screenshot you posted: It shows the error pretty well I would say.

[sayden]

Added some example config file for full reference :)

[ruflin]

Thank your for the addition of the docs.

I suggest to take out docs and magefile change into a separate PR for further discussion so we can get the field remove code in quickly to rebase the apache module on top of it. WDYT?

[ruflin]

No strong preference as long as the files written to disk are indented.

For the screenshot you posted: It shows the error pretty well I would say.

[ruflin]

Probably @andrewkroh knows best here.

[ruflin]

It's not correct that the server is launched on 5555, it's a random port selected but we hardcode 5555 in the final event.

[sayden]

Closed this by mistake, I cannot reopen it now 🤓

PR has been split in 3:

• README change [Metricbeat] Add README to mocked tests folder #11714
• Mage target [Metricbeat] Added mage target to run mocket tests #11715
• Mocked tests new config option [Metricbeat] Add remove fields option to mocked tests config #11716