diff --git a/test/9pm b/test/9pm
index 2b5dd6067..276451d44 160000
--- a/test/9pm
+++ b/test/9pm
@@ -1 +1 @@
-Subproject commit 2b5dd60678a7c70a34e8d6cc8d413fae8801c794
+Subproject commit 276451d440ceb5972b573607cce67f8e458f147c
diff --git a/test/9pm-proj.yaml b/test/9pm-proj.yaml
index 963e6f053..4c2b86b9a 100644
--- a/test/9pm-proj.yaml
+++ b/test/9pm-proj.yaml
@@ -2,3 +2,6 @@
   PROJECT-NAME: "Infix"
   PROJECT-ROOT: "../../"
   PROJECT-TOPDOC: "../case/"
+  AGENT-HINTS: |
+    Read test/infix-test-skill.md first, it explains how the tests work
+    and where to look.
diff --git a/test/infix-test-skill.md b/test/infix-test-skill.md
new file mode 100644
index 000000000..a6a5f53a4
--- /dev/null
+++ b/test/infix-test-skill.md
@@ -0,0 +1,17 @@
+# Infix test skill
+
+Info about the Infix regression tests.
+
+- Tests live under `test/case/`, are written in Python and use the infamy
+  framework in `test/infamy/`.
+- A test is a chain of `test.step()` blocks that configure one or more DUTs
+  over NETCONF or RESTCONF and verify the result with real traffic. The step
+  text in the failing TAP line is where to start reading.
+- DUTs run Infix, either as virtual machines (Qeneth, `test/virt/`) or as real
+  hardware. The fault is often in the product rather than the test. Device code
+  is in `src/`, YANG models in `src/confd/yang/`.
+- Each test has a logical `topology.dot` with names like `target:data`. Infamy
+  maps it onto the physical topology the test was given, honouring `requires`
+  and `provides` attributes, and prints the mapping in the log. A test is
+  skipped when no mapping fits.
+- Logs: `test/.log/<log id>/output/`. Full guide: `doc/testing.md`.