Add tests

[yyuu]

I added tests for sbt-extras with using sstephenson/bats, which is a testing framework for bash projects. Plus, I fixed some potential problems in sbt-extras to pass tests.

1. Set sbt.global.base for pre-0.13
2. Skip adding empty string as sbt argument when $log_level == "Info"
3. Download older releases of sbt-launch.jar if specified
4. Quote bash variables to avoid unexpected expansion

[yyuu]

You can run the tests with following procedures.

$ git clone https://github.com/sstephenson/bats.git
$ bats/bin/bats ./test
1..68
ok 1 loads .sbt_completion.sh
ok 2 fails to start sbt on empty project
ok 3 starts sbt on empty project if -sbt-create was given
ok 4 downloads sbt 0.7.x
ok 5 downloads sbt 0.10.x
ok 6 downloads sbt 0.11.x (< 0.11.3) from org.scala-tools.sbt:sbt-launch
ok 7 downloads sbt 0.11.x (>= 0.11.3) from org-scala-sbt:sbt-launch
ok 8 downloads sbt 0.12.x
ok 9 downloads sbt 0.13.x
(... snip ...)

[jkleckner]

+1
I've used this version of sbt along with https://github.com/jkleckner/dotsbt

[paulp]

This looks awesome. I'll take a test run and let you know.

[paulp]

@yyuu Do you recall what specifically led you to restoring the code to download older launchers? It's supposed to be the case that the current launcher subsumes all older launchers. I have definitely found that to be untrue myself - so I'm glad to see it back - and launcher/project version mismatch has been fronted as a possible factor in my ongoing battles with .ivy2 corruption, but if there are additional reasons it would assist me to know them.

[paulp]

To have someone send a PR including a bunch of tests is the open source dream. Thanks!

[paulp]

Also I flipped on travis so you need not if you don't want to.

[yyuu]

@paulp I believe genuine sbt-launch.jar of older releases have 100% compatibility with themselves, even if sbt 0.13.x claims that it subsumes their functionality. Just using older sbt is the easiest way for me to build older sbt based projects.

[paulp]

I believe genuine sbt-launch.jar of older releases have 100% compatibility with themselves

Wise words.