Add test for generated code with prefix headers

The shortest service definition which uses prefix headers is AWS
DataExchange. It is several thousand lines of generated code, so we keep
the expected generated output in a file.

Author: jhosteny

test/aws_codegen_test.exs

@@ -14,6 +14,9 @@ defmodule AWS.CodeGenTest do
     }
   }
 
+  @service_spec_custom_headers_file "test/fixtures/apis_specs/dataexchange.json"
+  @service_spec_custom_headers_generated "test/fixtures/generated/data_exchange.ex"
+
   setup do
     service_specs =
       @service_spec_file
@@ -24,7 +27,7 @@ defmodule AWS.CodeGenTest do
   end
 
   describe "render/2" do
-    defp setup_context(language, specs, docs \\ nil) do
+    defp setup_context(language, specs, _docs \\ nil) do
       spec = %AWS.CodeGen.Spec{
         api: specs,
         module_name: "AWS.CloudTrailData",
@@ -37,6 +40,19 @@ defmodule AWS.CodeGenTest do
       RestService.load_context(language, spec, @endpoints_spec)
     end
 
+    defp setup_dataexchange_context(language, specs, _docs \\ nil) do
+      spec = %AWS.CodeGen.Spec{
+        api: specs,
+        module_name: "AWS.DataExchange",
+        filename: "data_exchange.ex",
+        protocol: :rest_json,
+        language: :elixir,
+        shape_name: "com.amazonaws.dataexchange#DataExchange"
+      }
+
+      RestService.load_context(language, spec, @endpoints_spec)
+    end
+
     test "renders the Elixir module with docs", %{specs: specs} do
       context = setup_context(:elixir, specs)
 
@@ -238,6 +254,7 @@ defmodule AWS.CodeGenTest do
                  def put_audit_events(%Client{} = client, input, options \\\\ []) do
                    url_path = \"/PutAuditEvents\"
                    headers = []
+                   custom_headers = []
 
                    {query_params, input} =
                      [
@@ -254,7 +271,7 @@ defmodule AWS.CodeGenTest do
                      :post,
                      url_path,
                      query_params,
-                     headers,
+                     custom_headers ++ headers,
                      input,
                      options,
                      200
@@ -717,6 +734,7 @@ defmodule AWS.CodeGenTest do
                  def put_audit_events(%Client{} = client, input, options \\\\ []) do
                    url_path = \"/PutAuditEvents\"
                    headers = []
+                   custom_headers = []
 
                    {query_params, input} =
                      [
@@ -733,7 +751,7 @@ defmodule AWS.CodeGenTest do
                      :post,
                      url_path,
                      query_params,
-                     headers,
+                     custom_headers ++ headers,
                      input,
                      options,
                      200
@@ -742,5 +760,22 @@ defmodule AWS.CodeGenTest do
                end
                """)
     end
+
+    test "renders the Elixir module with custom headers" do
+      specs_file =
+        @service_spec_custom_headers_file
+        |> File.read!()
+        |> Poison.decode!()
+
+      context = setup_dataexchange_context(:elixir, specs_file)
+
+      result =
+        context
+        |> AWS.CodeGen.render("priv/rest.ex.eex")
+        |> IO.iodata_to_binary()
+
+      generated = File.read!(@service_spec_custom_headers_generated)
+      assert result == generated
+    end
   end
 end