test: enable travis-ci with bats (#108)

- add .travis.yml.
- move bats fixtures to .bats extension, since it allows detection of test
files automatically by file extension.
- use BATS_TEST_DIRNAME variable to compute location of COMMAND.
- IMPORTANT: use `echo "$output">&2` before final check so that we can debug
  the test cases by their output

Ref #2.

Signed-off-by: Ahmet Alp Balkan <ahmetb@google.com>

.travis.yml

@@ -0,0 +1,8 @@
+before_install:
+  - sudo add-apt-repository ppa:duggan/bats --yes
+  - sudo apt-get update -qq
+  - sudo apt-get install -qq bats
+  - sudo curl -fsSL -o /usr/bin/kubectl https://storage.googleapis.com/kubernetes-release/release/v1.13.1/bin/linux/amd64/kubectl
+  - sudo chmod +x /usr/bin/kubectl 
+script:
+  - bats test/

test/kubectx.bats

@@ -1,6 +1,6 @@
 #!/usr/bin/env bats
 
-COMMAND=../kubectx
+COMMAND="$BATS_TEST_DIRNAME/../kubectx"
 
 @test "--help should not fail" {
   run ${COMMAND} --help

test/kubens.bats

@@ -1,13 +1,15 @@
 #!/usr/bin/env bats
 
-COMMAND=../kubens
+COMMAND="${BATS_TEST_DIRNAME}/../kubens"
 
 @test "--help should not fail" {
   run ${COMMAND} --help
+  echo "$output">&2
   [ "$status" -eq 0 ]
 }
 
 @test "-h should not fail" {
   run ${COMMAND} -h
+  echo "$output">&2
   [ "$status" -eq 0 ]
 }