Most of the tests use mocked servers as stand-ins for the exporters to send to.
The docker images are built and pushed to ECR as part of terraform/imagebuild and then used in the tests as part of defaults/docker_compose.tpl.
Most will use the https mocked_server, but some test cases like otlp_grpc_exporter_metric_mock and otlp_grpc_exporter_trace_mock will need to use the grpc_metrics and grpc_trace mocked_servers.
The servers themselves are very basic. They listen for a message and tend to set a flag to success upon receiving it. Typically, they are set up with two servers: one to mock the backend and one to report on the status of that mock (if endpoint is called, how many times, etc.). There's a built-in 15ms of latency between each message that's received. The status reporter will always be on port 8080 and support the :8080/ (returns "healthcheck") and the :8080/check-data (returns "success" if mock has received messages) endpoints.