[docs] add document for running BR tests locally (#7044)

script/test

@@ -51,6 +51,7 @@ readonly INTER_OP_BBR="${INTER_OP_BBR:-1}"
 readonly OT_COREDUMP_DIR="${PWD}/ot-core-dump"
 readonly FULL_LOGS=${FULL_LOGS:-0}
 readonly TREL=${TREL:-0}
+readonly LOCAL_OTBR_DIR=${LOCAL_OTBR_DIR:-""}
 
 build_simulation()
 {
@@ -296,7 +297,12 @@ do_build_otbr_docker()
     otdir=$(pwd)
 
     (
-        ./script/git-tool clone https://github.com/openthread/ot-br-posix.git --depth 1 "${otbrdir}"
+        if [[ -z ${LOCAL_OTBR_DIR} ]]; then
+            ./script/git-tool clone https://github.com/openthread/ot-br-posix.git --depth 1 "${otbrdir}"
+        else
+            cp -r "${LOCAL_OTBR_DIR}"/* "${otbrdir}"
+            rm -rf "${otbrdir}"/build
+        fi
         cd "${otbrdir}"
         rm -rf third_party/openthread/repo
         cp -r "${otdir}" third_party/openthread/repo

tests/scripts/thread-cert/border_router/README.md

@@ -0,0 +1,25 @@
+# OpenThread Border Router Tests
+
+## Run Border Router (BR) tests locally
+
+BR tests run in isolated Docker network and containers, so a new OTBR Docker image needs to be created before running these tests:
+
+```shell
+# Use root privilege when necessary.
+
+# Download OpenThread's branch of wireshark. Run this for the first time.
+./script/test get_thread_wireshark
+
+# Clear current OpenThread directory (remember to add new source files).
+git clean -xfd
+
+# Rebuild the OTBR Docker image if OTBR source code is updated.
+LOCAL_OTBR_DIR=$HOME/ot-br-posix ./script/test build_otbr_docker
+
+# Build simulated OpenThread firmware.
+VIRTUAL_TIME=0 ./script/test build
+
+# Run the BR tests locally.
+TEST_CASE=./tests/scripts/thread-cert/border_router/test_advertising_proxy.py
+VERBOSE=1 PACKET_VERIFICATION=1 VIRTUAL_TIME=0 ./script/test cert_suite ${TEST_CASE}
+```