`ChangePointDetector` doesn't detect a spike

[przemekwitek]

Elasticsearch Version

main

Installed Plugins

No response

Java Version

bundled

OS Version

MacOS

Problem Description

ChangePointDetector class does not detect a spike for a constant function with one spike

Steps to Reproduce

Using a unit test, I wanted to obtain a "spike" from a ChangePointDetector. The data I used (25 data points with a spike in the middle):
51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 500001, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51, 51
The spike did not get detected.
When I added randomness (replaced 51 with randomLongBetween(50, 53) the spike got detected.

Logs (if relevant)

No response

[elasticsearchmachine]

Pinging @elastic/ml-core (Team:ML)

[przemekwitek]

@jan-elastic and @tveasey for visibility