Fill in testing Dockerfile stub.

blimp/engine/testing/Dockerfile

Index: blimp/engine/testing/Dockerfile
diff --git a/blimp/engine/testing/Dockerfile b/blimp/engine/testing/Dockerfile
index 711535347dce4aa52f8bb5e3a6fc7314a5f3f357..3575c4eab90e606ce15cb7b93e361bebcb46023a 100644
--- a/blimp/engine/testing/Dockerfile
+++ b/blimp/engine/testing/Dockerfile
@@ -1,2 +1,12 @@
-# Testing dockerfile stub
-# TODO(jessicag): Fill in (crbug.com/616945).
+# Testing filesystem setup. Built from share setup with engine Dockerfile.

[maniscalco, 2016/07/11 22:55:24]

I'm having a hard time parsing this comment.  Can you reword?  Maybe something
like:

"This Dockerfile is used to build an image containing Blimp Engine test and
tests for dependencies of Blimp Engine. It is built on a base image
(base:latest) that's also used for running the Engine itself."

[Jess, 2016/07/11 23:15:33]

Updated comment.

I am avoiding saying it builds an image because that isn't actually what is used
to run tests. It is a service detail, but one that informs what should be
included in this Dockerfile.

+FROM base:latest
+
+RUN mkdir -p /out/test/

[maniscalco, 2016/07/11 22:55:24]

What's the thinking behind the directory structure?  Do you anticipate having
other subdirs under /out?  Would /test be simpler?

[Jess, 2016/07/11 23:15:33]

The test binaries by default assume src is down two directories. Something that
can be easily handled by flags in the service, but I wanted to cut down on the
gotchas while hooking everything together.

[maniscalco, 2016/07/11 23:21:17]

Ah, I see.  OK, I suggest adding a comment here to that effect.  That ways it's
clear that this isn't an arbitrary directory structure.

+
+# The glob below expands to all files, but does not add directories
+# recursively.
+ADD * /out/test/
+
+RUN chown -R blimp_user /out/test/
+
+USER blimp_user