Test runner config values not properly detected

[raphaeltm]

The test runner does not properly identify config values that are used in string interpolation. For example, in the following compose file:

services:
  hasura:
    restart: unless-stopped
    build:
      dockerfile: Dockerfile
      context: ./hasura
    # If you want to add your own domain name in Defang BYOC, uncomment the following line and replace the domain name with your own
    # domainname: hasura.mycoolapp.com
    ports:
      - target: 8080
        published: 8080
        mode: ingress
    depends_on:
      database:
        condition: service_started
    environment:
      - HASURA_GRAPHQL_ADMIN_SECRET
      - HASURA_GRAPHQL_DATABASE_URL=postgres://postgres:${POSTGRES_PASSWORD}@database:5432/postgres?sslmode=${SSL_MODE}
      - HASURA_GRAPHQL_ENABLE_CONSOLE=true
      - HASURA_GRAPHQL_UNAUTHORIZED_ROLE=public
      - HASURA_GRAPHQL_EXPERIMENTAL_FEATURES=naming_convention
      - HASURA_GRAPHQL_DEFAULT_NAMING_CONVENTION=graphql-default
      - HASURA_GRAPHQL_MIGRATIONS_DIR=/hasura/migrations
      - HASURA_GRAPHQL_METADATA_DIR=/hasura/metadata
  
  database:
    image: postgres:16
    x-defang-postgres: true
    ports:
      - target: 5432
        mode: host
    environment:
      - POSTGRES_PASSWORD

It does not detect SSL_MODE so tests always fail. The following is the current workaround:

      - SSL_MODE

That allows it to be detected and thus load the correct secret from the test environment.

[raphaeltm]

I propose that we include a .env.testing file in each sample that requires it. This makes it easier to develop samples, could be useful to end users as well if they want to run tests on their compose projects, and would reduce the amount of stuff that needs to be coordinated between GitHub settings, the testing workflow, and the samples. The test runner would simply append --env-file=.env.testing if the file exists.