With at least two endpoints and Traffic Policy, you can run simple A/B tests with using the rand.double() macro.

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Basic example

This rule:
  1. Uses rand.double() to generate a random double between 0 and 1 when traffic reaches the endpoint
  2. Checks if the value is less than or equal to 0.5
  3. If so, it routes the traffic to a different internal agent endpoint.
on_http_request:
  -     expressions:
      - rand.double() <= 0.5
    actions:
      -         type: forward-internal
        config:
          url: https://a.internal
  -     actions:
      -         type: forward-internal
        config:
          url: https://b.internal
You can change the value the random number is checked against to split the traffic in different ratios. For example,>=0.8 would send 80% of the traffic to one endpoint and 20% to the other.
See the forward-internal Traffic Policy action docs for more information.

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Using rewrites

You can also send the traffic to a different route using url rewrites. 
on_http_request:
  -     expressions:
      - rand.double() <= 0.5
    actions:
      -         type: url-rewrite
        config:
          from: /path/to/test
          to: /path/to/test-b
  -     actions:
      -         type: forward-internal
        config:
          url: https://b.internal
See the URL Rewrite Example for another example using rewrites.