1 files changed, 65 insertions, 0 deletions
diff --git a/share/python/lib/daemon.md b/share/python/lib/daemon.md
index c4f5e27..c7bb49f 100644
--- a/share/python/lib/daemon.md
+++ b/share/python/lib/daemon.md
@@ -111,6 +111,71 @@ echo hola 1>&2
 echo hi there
 ~~~
 
+# Can specify additional environment variables for daemon
+
+Some daemons are configured through their environment rather than configuration
+files. This scenario verifies that a step can set arbitrary variables in the
+daemon's environment.
+
+~~~scenario
+when I start "/usr/bin/env" as a background process as env, with environment {"custom_variable": "has a Value"}
+when daemon env has produced output
+when I stop background process env
+then daemon env stdout contains "custom_variable=has a Value"
+~~~
+
+~~~scenario
+given a daemon helper shell script env-with-port.py
+when I try to start "./env-with-port.py 8765" as env-with-port, on port 8765, with environment {"custom_variable": "1337"}
+when I stop background process env-with-port
+then daemon env-with-port stdout contains "custom_variable=1337"
+~~~
+
+~~~scenario
+given a daemon helper shell script env-with-port.py
+when I start "./env-with-port.py 8766" as a background process as another-env-with-port, on port 8766, with environment {"subplot2": "000"}
+when daemon another-env-with-port has produced output
+when I stop background process another-env-with-port
+then daemon another-env-with-port stdout contains "subplot2=000"
+~~~
+
+It's important that these new environment variables are not inherited by the
+steps that follow. To verify that, we run one more scenario which *doesn't* set
+any variables, but checks that none of the variables we mentioned above are
+present.
+
+~~~scenario
+when I start "/usr/bin/env" as a background process as env2
+when daemon env2 has produced output
+when I stop background process env2
+then daemon env2 stdout doesn't contain "custom_variable=has a Value"
+then daemon env2 stdout doesn't contain "custom_variable=1337"
+then daemon env2 stdout doesn't contain "subplot2=000"
+~~~
+
+~~~{#env-with-port.py .file .python .numberLines}
+#!/usr/bin/env python3
+
+import os
+import socket
+import sys
+import time
+
+for (key, value) in os.environ.items():
+    print(f"{key}={value}")
+
+port = int(sys.argv[1])
+print(f"port is {port}")
+
+s = socket.socket()
+s.bind(("127.0.0.1", port))
+s.listen()
+
+(conn, _) = s.accept()
+conn.recv(1)
+s.close()
+~~~
+
 
 ---
 title: Acceptance criteria for the lib/daemon Subplot library