tests: add a test for dockerfile-path

tests/apps/dockerfile/second.Dockerfile

@@ -0,0 +1,15 @@
+FROM node:4-alpine
+
+RUN apk add --no-cache bash
+
+EXPOSE 3001/udp
+EXPOSE  3000/tcp
+EXPOSE 3003
+
+COPY . /var/www/html
+WORKDIR /var/www/html
+RUN npm install
+
+RUN echo hi
+
+CMD npm start

tests/unit/builder-dockerfile.bats

@@ -0,0 +1,50 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+setup() {
+  create_app
+}
+
+teardown() {
+  destroy_app
+}
+
+@test "(builder-dockerfile:set)" {
+  run deploy_app dockerfile
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku builder-dockerfile:set $TEST_APP dockerfile-path nonexistent-dockerfile"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku ps:rebuild $TEST_APP"
+  echo "output: $output"
+  echo "status: $status"
+  assert_failure
+
+  run /bin/bash -c "dokku builder-dockerfile:set $TEST_APP dockerfile-path second.Dockerfile"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku ps:rebuild $TEST_APP"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output_contains 'echo hi'
+
+  run /bin/bash -c "dokku builder-dockerfile:set $TEST_APP dockerfile-path"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku ps:rebuild $TEST_APP"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output_contains 'echo hi' 0
+}