Run versionLT tests in the image we are building

OS X sort doesn't have -V
Ensure the sort in the image, not the one in the build machine, works
diff --git a/tests/functions.bats b/tests/functions.bats
index 6745b10..b89de8c 100644
--- a/tests/functions.bats
+++ b/tests/functions.bats
@@ -1,24 +1,31 @@
 #!/usr/bin/env bats
 
+SUT_IMAGE=bats-jenkins
+
 load 'test_helper/bats-support/load'
 load 'test_helper/bats-assert/load'
 load test_helpers
 
 . $BATS_TEST_DIRNAME/../jenkins-support
 
+@test "build image" {
+  cd $BATS_TEST_DIRNAME/..
+  docker build -t $SUT_IMAGE .
+}
+
 @test "versionLT" {
-  run versionLT 1.0 1.0
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.0 1.0"
   assert_failure
-  run versionLT 1.0 1.1
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.0 1.1"
   assert_success
-  run versionLT 1.1 1.0
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.1 1.0"
   assert_failure
-  run versionLT 1.0-beta-1 1.0
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.0-beta-1 1.0"
   assert_success
-  run versionLT 1.0 1.0-beta-1
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.0 1.0-beta-1"
   assert_failure
-  run versionLT 1.0-alpha-1 1.0-beta-1
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.0-alpha-1 1.0-beta-1"
   assert_success
-  run versionLT 1.0-beta-1 1.0-alpha-1
+  run docker run -ti --rm $SUT_IMAGE bash -c "source /usr/local/bin/jenkins-support && versionLT 1.0-beta-1 1.0-alpha-1"
   assert_failure
 }