add tests for diffing

test/integration/diffing3/setup.sh

@@ -0,0 +1,38 @@
+#!/bin/sh
+
+cd $1
+
+git init
+
+git config user.email "CI@example.com"
+git config user.name "CI"
+
+echo test0 > file0
+git add .
+git commit -am file0
+
+echo test1 > file1
+git add .
+git commit -am file1
+
+echo test2 > file2
+git add .
+git commit -am file2
+
+echo "line one" > file4
+git add .
+git commit -am file4
+
+git checkout -b branch2
+
+echo "line two" >> file4
+git add .
+git commit -am file4
+
+echo "line three" >> file4
+git add .
+git commit -am file4
+
+echo "line two" >> file2
+git add .
+git commit -am file2