Describe how to reproduce CI

doc/TESTBenches.md

@@ -165,3 +165,53 @@ Webhook ~documentation ~BUILD-ONLY ~4G-LTE ~5G-NR
 - [RAN-SA-Module-CN5G](https://jenkins-oai.eurecom.fr/view/RAN/job/RAN-SA-Module-CN5G/)
   - asterix + N310 (gNB), nrmodule2 + Quectel, porcepix w/ OAI 5GC
   - NR 2x2 (standalone)
+
+## How to reproduce CI results
+
+The CI builds docker images at the beginning of every test run. To see the
+exact command line steps, please refer to the `docker/Dockerfile.build.*`
+files. Note that the console log of each pipeline run also lists the used
+docker files.
+
+The CI uses these images for *most* of the pipelines. It uses docker-compose to
+orchestrate the images. To identify the docker-compose file, follow these
+steps:
+
+1. Each CI test run HTML lists the XML file used for a particular test run.
+   Open the corresponding XML file under `ci-scripts/xml_files/`.
+2. The XML file has a "test case" that refers to deployment of the image; it
+   will reference a directory containing a YAML file (the docker-compose file)
+   using option `yaml_path`, which will be under `ci-scripts/yaml_files/`. Go
+   to this directory and open the docker-compose file.
+3. The docker-compose file can be used to run images locally, or you can infer
+   the used configuration file and possible additional options that are to be
+   passed to the executable to run from source.
+
+For instance, to see how the CI runs the multi-UE 5G RFsim test case, the above
+steps look like this:
+
+1. The first tab in the 5G RFsim test mentions
+   `xml_files/container_5g_rfsim.xml`, so open
+   `ci-scripts/xml_files/container_5g_rfsim.xml`.
+2. This XML file has a `DeployGenObject` test case, referencing the directory
+   `yaml_files/5g_rfsimulator`. The corresponding docker-compose file path is
+   `ci-scripts/yaml_files/5g_rfsimulator/docker-compose.yaml`.
+3. To know how to run the gNB, realize that there is a section `oai-gnb`. It
+   mounts the configuration
+   `ci-scripts/conf_files/gnb.sa.band78.106prb.rfsim.conf` (note that the path
+   is relative to the directory in which the docker-compose file is located).
+   Further, an environment variable `USE_ADDITIONAL_OPTIONS` is declared,
+   referencing the relevant options `--sa -E --rfsim` (you can ignore logging
+   options). You would therefore run the gNB from source like this:
+   ```
+   sudo ./cmake_targets/ran_build/build/nr-softmodem -O ci-scripts/conf_files/gnb.sa.band78.106prb.rfsim.conf --sa -E --rfsim
+   ```
+   To run this on your local machine, assuming you have a 5GC installed, you
+   might need to change IP information in the config to match your core.
+
+If you wish, you can rebuild CI images locally following [these
+steps](../docker/README.md) and then use the docker-compose file directly.
+
+Some tests are run from source (e.g.
+`ci-scripts/xml_files/gnb_phytest_usrp_run.xml`), which directly give the
+options they are run with.