Add tests of cache bind directory

tests/unit/20_build-env.bats

@@ -70,3 +70,28 @@ teardown() {
   echo "status: "$status
   assert_output "herokuish"
 }
+
+@test "(build-env) DOKKU_ROOT cache bind is used by default" {
+  deploy_app
+
+  BUILD_CID=$(docker ps -a |grep $TEST_APP |grep /bin/bash | awk '{print $1}')
+  run /bin/bash -c "docker inspect --format '{{ .HostConfig.Binds }}' $BUILD_CID | tr -d '[]' | cut -f1 -d:"
+  echo "output: "$output
+  echo "status: "$status
+  assert_output "$DOKKU_ROOT/$TEST_APP/cache"
+}
+
+@test "(build-env) DOKKU_HOST_ROOT cache bind is used if set" {
+  TMP_ROOT=$(mktemp -d)
+  mkdir -p $DOKKU_ROOT/.dokkurc
+  echo export DOKKU_HOST_ROOT="$TMP_ROOT" > $DOKKU_ROOT/.dokkurc/HOST_ROOT
+  DOKKU_HOST_ROOT="$TMP_ROOT" deploy_app
+
+  BUILD_CID=$(docker ps -a |grep $TEST_APP |grep /bin/bash | awk '{print $1}')
+  run /bin/bash -c "docker inspect --format '{{ .HostConfig.Binds }}' $BUILD_CID | tr -d '[]' | cut -f1 -d:"
+  echo "output: "$output
+  echo "status: "$status
+  assert_output "$TMP_ROOT/$TEST_APP/cache"
+
+  rm -rf $TMP_ROOT $DOKKU_ROOT/.dokkurc/HOST_ROOT
+}