[system testing] Validate assertion for expected number of events

[djptek]

What does this PR do?

This PR will validate system testing through the addition of an assertion for expected number of events

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
  - [ ] I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
  - [ ] I have verified that Kibana version constraints are current according to guidelines.

Author's Checklist

• Wait for the outcome of the elastic-package PR [system testing] Implement assertion for expected number of events since these changes lack meaning outside that context.

How to test this PR locally

Ensure elastic-package is up to date by running

make install

in the ./elastic-package root directory of an up-to-date clone or synced fork of this repository

In the integrations repository, run the following commands from the ./integrations root directory

cd ../httpjson
elastic-package stack down -v
elastic-package build -v
elastic-package stack up --version 8.5.0-SNAPSHOT -v -d
elastic-package test system -v

Validate that the output contains:

• Debug entries similar to the following:

2022/11/22 20:12:47 DEBUG running test with configuration 'expected-event-count'
2022/11/22 20:12:47 DEBUG setting up service...
...
2022/11/22 20:13:07 DEBUG checking for expected data in data stream...
2022/11/22 20:13:07 DEBUG found 1 hits in logs-httpjson.generic-ep data stream
2022/11/22 20:13:07 DEBUG found 3 events under "parent"

(The assertion found 3 events under "parent" will only triggered after the related elastic-package PR has merged)

• A Test result similar to the following:

  │ httpjson │ generic │ system │ expected-event-count │ PASS │ 20.829026099s │

Related issues

• Relates [system testing] Add assertion for expected number of events elastic-package#821

## Screenshots

[elasticmachine]

💚 Build Succeeded

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Build stats

• Start Time: 2022-12-23T15:49:28.906+0000

• Duration: 17 min 53 sec

Test stats 🧪

Test	Results
Failed	0
Passed	8
Skipped	0
Total	8

🤖 GitHub comments

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (0/0)	💚
Files	100.0% (0/0)	💚 1.705
Classes	100.0% (0/0)	💚 1.705
Methods	100.0% (3/3)	💚 8.6
Lines	100.0% (0/0)	💚 7.11
Conditionals	100.0% (0/0)	💚

[botelastic]

Hi! We just realized that we haven't looked into this PR in a while. We're sorry! We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1. Thank you for your contribution!

[botelastic]

Hi! We just realized that we haven't looked into this PR in a while. We're sorry! We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1. Thank you for your contribution!