Add chaos behavior for probabilistic fault injection

[tugkanboz]

Closes #918.

Adds a chaos behavior to the existing _behaviors framework. It probabilistically injects errors (replacing the response with an error status code) and/or random latency. Both are independent and all fields default to 0, so the behavior is a no-op unless explicitly configured. No new dependencies, just Math.random.

Example:

{
  "responses": [{ "is": { "statusCode": 200, "body": "ok" } }],
  "_behaviors": {
    "chaos": {
      "errorRate": 0.1,
      "errorStatusCode": 503,
      "latencyRate": 0.05,
      "maxLatencyMs": 1000
    }
  }
}

Changes:

• behavior + validation schema in src/models/behaviors.js
• 12 unit tests in test/models/behaviors/chaosTest.js
• doc page src/views/docs/api/behaviors/chaos.ejs plus entry in behaviors.ejs

All 750 existing unit tests still pass and lint is clean.

Naming question from #918 is still open: chaos, fault, or faults? Happy to rename before merge.

[mattherman]

Hoping to have time to look at this soon - apologies for letting it sit. It seems like a reasonable idea.

[tugkanboz]

Thanks @mattherman, no rush. Looking forward to your feedback.

[sonarqubecloud]

Quality Gate failed

Failed conditions
3 Security Hotspots

See analysis details on SonarQube Cloud

[tugkanboz]

Hi @mattherman , just checking in. Have you had a chance to review this PR?

Please let me know if there’s anything I should update or change. Thanks!

[tugkanboz]

Thanks for the thorough review, @mattherman! Pushed changes addressing all the feedback:

• Reworked the errorRate: 0 / maxLatencyMs: 0 tests to use a non-zero random draw, so they actually validate the config rather than a low random draw
• Added the missing latencyRate validation test
• maxLatencyMs now defaults to 1000ms instead of being a silent no-op when only latencyRate is set
• Docs now clarify chaos error injection is HTTP/HTTPS-only, with a link to the fault response for TCP
• Dropped "faults" wording in the docs to avoid confusion with the fault response
• Turned the docs example into an actual documentation test (deterministic, errorRate: 1)
• Added API tests in mbTest/api/http/httpBehaviorsTest.js

Left the status code range validation as a follow-up per your note. Let me know if anything else needs adjusting.

[sonarqubecloud]

Quality Gate failed

Failed conditions
C Security Rating on New Code (required ≥ A)

See analysis details on SonarQube Cloud

Catch issues before they fail your Quality Gate with our IDE extension SonarQube for IDE