From 0d40fd7552e826aa6ce860d101a5bd49548ed785 Mon Sep 17 00:00:00 2001
From: Simon Hafner <hafnersimon@gmail.com>
Date: Thu, 18 Jun 2015 13:51:29 -0500
Subject: [PATCH] explained how to run the tester to compare commits

---
 contributing.md | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/contributing.md b/contributing.md
index 123fd5668e..66a57971c0 100644
--- a/contributing.md
+++ b/contributing.md
@@ -89,4 +89,27 @@ which will run a good subset of tests. Some tests may fail.
 Because some tests fail in the current `devel` branch, not every fail
 after your change is necessarily caused by your changes.
 
-TODO
+The tester can compare two test runs. First, you need to create the
+reference test. You'll also need to the commit id, because that's what
+the tester needs to know in order to compare the two.
+
+```bash
+git checkout devel
+DEVEL_COMMIT=$(git rev-parse HEAD)
+./koch tests
+```
+
+Then switch over to your changes and run the tester again.
+
+```bash
+git checkout your-changes
+./koch tests
+```
+
+Then you can ask the tester to create a `testresults.html` which will
+tell you if any new tests passed/failed.
+
+```bash
+./koch html $DEVEL_COMMIT
+(xdg-)open testresults.html
+```