Graphql Query testing doesn't return correctly the result in Phoenix

Hello everyone I'm just new to Elixir, generally new to FP. So basically I try to learn Elixir and afterwards jump to building a graphql api server.

I read and follow the book "Craft GraphQL APIs in Elixir with Absinthe" and stuck at the testing of a graphql query.

Here's what the book said:

test "menuItems field returns menu items" do
  conn = build_conn()
  conn = get conn, "/api", query: @query
  assert json_response(conn, 200) == %{
   "data" => %{
     "menuItems" => [
       //key-value pair
     ]
   }
  }
end

Here's what the I attempt , I noticed that in my local machine when I make a query it uses POST method rather than GET method so I change it to post instead:

@query """
{
  courses {
    name
  }
}
"""

test "courses field returns courses" do
  conn = build_conn()
  conn = post conn, "/api/graphiql", query: @query
  assert json_response(conn, 200) === %{
    "data" => %{
      "courses" => [
        %{"name" => "BSIT"},
        %{"name" => "BSCS"},
        %{"name" => "BSBA"}
      ]
    }
  }
end

Then when I run the test it fails because the query returns empty result.

Assertion with === failed
  code:  assert json_response(conn, 200) === %{"data" => %{"courses" => [%{"name" => "BSIT"}, %{"name" => "BSCS"}, %{"name" => "BSBA"}]}}
  left:  %{"data" => %{"courses" => []}}
  right: %{"data" => %{"courses" => [%{"name" => "BSIT"}, %{"name" => "BSCS"}, %{"name" => "BSBA"}]}}
  stacktrace:
    test/voting_system_web/query/course_test.exs:15: (test)

Then I try testing the query through curl and the query works and returns a result.

 curl -X POST -H "Content-Type: application/json" --data '{ "query": "{ courses { name } }"}' http://localhost:4000/api/graphiql
 {"data":{"courses":[{"name":"BSIT"},{"name":"BSCS"},{"name":"BSBA"}]}}%

Solution

Have you already checked whether your test database contains the same data as your dev database? The default way in Phoenix is to use different environments for test/dev/prod and therefore you should find the respective .exs file within the config folder of your project and this is also where your database connection for the test/dev/prod environment is defined.

When you start Phoenix with iex -S mix phx.server your environment should be dev per default (if your MIX_ENV is empty).

Just for the sake of completeness: You can execute MIX_ENV=test iex -S mix phx.server then you would use the test environment and you can therefore check with your CURL command if your query returns a result for the test environment/database.