Auto DevOps test job fails on simple project (unable to select buildpack)

Summary

(Summarize the bug encountered concisely)

Steps to reproduce

I have a very simple hello world project at https://gitlab.com/jlenny/product_walkthrough_1. I enabled Auto DevOps and the first pipeline failed with the following error:

$ if [ -z ${KUBERNETES_PORT+x} ]; then # collapsed multi-line command
$ export DATABASE_URL="postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@${DB_HOST}:5432/${POSTGRES_DB}"
$ cp -R . /tmp/app
$ /bin/herokuish buildpack test
-----> Unable to select a buildpack

Example Project

https://gitlab.com/jlenny/product_walkthrough_1

What is the current bug behavior?

Test job fails

What is the expected correct behavior?

Test job passes, or at least doesn't run if it's dependent on having a k8s cluster

Relevant logs and/or screenshots

$ if [ -z ${KUBERNETES_PORT+x} ]; then # collapsed multi-line command
$ export DATABASE_URL="postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@${DB_HOST}:5432/${POSTGRES_DB}"
$ cp -R . /tmp/app
$ /bin/herokuish buildpack test
-----> Unable to select a buildpack

Output of checks

This bug happens on GitLab.com

Possible fixes

Use language detection rules like the parent template, but change the top two rules to

- - if: '$BUILDPACK_URL || $AUTO_DEVOPS_EXPLICITLY_ENABLED == "1"'
- - exists:
-   - Dockerfile
+ - if: '$BUILDPACK_URL'