elixir - Handling configuration values in mix -

i struggling handle config values in mix (particularly when running tests). scenario:

• i have client library, common config values (key, secret, region).
• i want test happens when there's no region value setup
• i have no test.exs file in /config

i'm doing (and doesn't work). module being tested (simplified):

defmodule streamex.client   @api_region application.get_env(:streamex, :region)   @api_key application.get_env(:streamex, :key)   @api_secret application.get_env(:streamex, :secret)   @api_version "v1.0"   @api_url "api.getstream.io/api"    def full_url(%request{} = r)     url = <<"?api_key=", @api_key :: binary>>   end end 

test:

setup_all   streamex.start   application.put_env :streamex, :key, "key"   application.put_env :streamex, :secret, "secret"   application.put_env :streamex, :secret, "" end 

what happens when running mix test main module, sets attributes values, throws following error since can't find valid values:

lib/streamex/client.ex:36: invalid literal nil in <<>> 

i'm still starting may seem obvious, can't find solution after reading docs.

the problem you're storing return value of application.get_env in module attribute, evaluated @ compile time. if change values in tests, won't reflected in module attribute -- you'll value that's present when mix compiled module, includes evaluating config/config.exs , modules mix compiled before compiling module. fix move variables can changed function , call functions whenever they're used:

defmodule streamex.client   @api_version "v1.0"   @api_url "api.getstream.io/api"    def full_url(%request{} = r)     url = <<"?api_key=", api_key :: binary>>   end    def api_region, do: application.get_env(:streamex, :region)   def api_key, do: application.get_env(:streamex, :key)   def api_secret, do: application.get_env(:streamex, :secret) end 

note if library , want users of library able configure values in config files, have use function calls @ runtime dependencies of app compiled before app.