From 7c3408d1a88a24c2db917ab48cb15d13ac683427 Mon Sep 17 00:00:00 2001
From: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
Date: Mon, 10 Jan 2022 17:06:42 +0000
Subject: [PATCH] Document the `SYNAPSE_TEST_PERSIST_SQLITE_DB` unit test env
 var (#11715)

---
 changelog.d/11715.doc                  |  1 +
 docs/development/contributing_guide.md | 21 +++++++++++++++++++++
 2 files changed, 22 insertions(+)
 create mode 100644 changelog.d/11715.doc

diff --git a/changelog.d/11715.doc b/changelog.d/11715.doc
new file mode 100644
index 0000000000..32b7c10b0b
--- /dev/null
+++ b/changelog.d/11715.doc
@@ -0,0 +1 @@
+Document the new `SYNAPSE_TEST_PERSIST_SQLITE_DB` environment variable in the contributing guide.
diff --git a/docs/development/contributing_guide.md b/docs/development/contributing_guide.md
index abdb808438..121f7c0687 100644
--- a/docs/development/contributing_guide.md
+++ b/docs/development/contributing_guide.md
@@ -169,6 +169,27 @@ To increase the log level for the tests, set `SYNAPSE_TEST_LOG_LEVEL`:
 SYNAPSE_TEST_LOG_LEVEL=DEBUG trial tests
 ```
 
+By default, tests will use an in-memory SQLite database for test data. For additional
+help with debugging, one can use an on-disk SQLite database file instead, in order to
+review database state during and after running tests. This can be done by setting
+the `SYNAPSE_TEST_PERSIST_SQLITE_DB` environment variable. Doing so will cause the
+database state to be stored in a file named `test.db` under the trial process'
+working directory. Typically, this ends up being `_trial_temp/test.db`. For example:
+
+```sh
+SYNAPSE_TEST_PERSIST_SQLITE_DB=1 trial tests
+```
+
+The database file can then be inspected with:
+
+```sh
+sqlite3 _trial_temp/test.db
+```
+
+Note that the database file is cleared at the beginning of each test run. Thus it 
+will always only contain the data generated by the *last run test*. Though generally
+when debugging, one is only running a single test anyway.
+
 ### Running tests under PostgreSQL
 
 Invoking `trial` as above will use an in-memory SQLite database. This is great for