Add some trivial tests for git-if-needed.

Change-Id: I5f8fde2aebb3ab051aa5afbc7d5a093f454cfbbb
diff --git a/tools/git-if-needed/tests/data/another-file.patch b/tools/git-if-needed/tests/data/another-file.patch
new file mode 100644
index 0000000..6cd5bce
--- /dev/null
+++ b/tools/git-if-needed/tests/data/another-file.patch
@@ -0,0 +1,21 @@
+From 2c8b59ff960b22a39f143ce1667963c259bb2bcc Mon Sep 17 00:00:00 2001
+From: Peter Penchev <openstack-dev@storpool.com>
+Date: Tue, 3 Dec 2019 12:31:35 +0200
+Subject: [PATCH] Add another file.
+
+Change-Id: I4953764f89bbac8b8d939657356c68c81255f1b4
+---
+ TODO.txt | 1 +
+ 1 file changed, 1 insertion(+)
+ create mode 100644 TODO.txt
+
+diff --git a/TODO.txt b/TODO.txt
+new file mode 100644
+index 0000000..bd1ee7c
+--- /dev/null
++++ b/TODO.txt
+@@ -0,0 +1 @@
++Do some things.
+-- 
+2.24.0
+