Raise an exception when trying to resolve a remote schema without a r…

…emote schema resolver

README.md

@@ -10,7 +10,7 @@ Add the project to your Mix dependencies in `mix.exs`:
 
 ```elixir
 defp deps do
-  [{:ex_json_schema, "~> 0.5.2"}]
+  [{:ex_json_schema, "~> 0.5.3"}]
 end
 ```
 

lib/ex_json_schema/schema.ex

@@ -7,6 +7,10 @@ defmodule ExJsonSchema.Schema do
     defexception message: "invalid schema"
   end
 
+  defmodule UndefinedRemoteSchemaResolverError do
+    defexception message: "trying to resolve a remote schema but no remote schema resolver function is defined"
+  end
+
   alias ExJsonSchema.Schema.Draft4
   alias ExJsonSchema.Schema.Root
 
@@ -162,7 +166,7 @@ defmodule ExJsonSchema.Schema do
   end
 
   defp remote_schema_resolver do
-    Application.get_env(:ex_json_schema, :remote_schema_resolver)
+    Application.get_env(:ex_json_schema, :remote_schema_resolver) || fn _url -> raise UndefinedRemoteSchemaResolverError end
   end
 
   defp assert_reference_valid(path, root, _ref) do

mix.exs

@@ -4,7 +4,7 @@ defmodule ExJsonSchema.Mixfile do
   def project do
     [
       app: :ex_json_schema,
-      version: "0.5.2",
+      version: "0.5.3",
       elixir: "~> 1.0",
       description: "A JSON Schema validator with full support for the draft 4 specification and zero dependencies.",
       deps: deps,

test/ex_json_schema/config_test.exs

@@ -0,0 +1,13 @@
+defmodule ExJsonSchema.ConfigTest do
+  use ExUnit.Case
+
+  import ExJsonSchema.Schema, only: [resolve: 1]
+
+  test "raising an exception when trying to resolve a remote schema and no remote schema resolver is defined" do
+    resolver = Application.get_env(:ex_json_schema, :remote_schema_resolver)
+    Application.put_env(:ex_json_schema, :remote_schema_resolver, nil)
+    schema = %{"$ref" => "http://somewhere/schema.json"}
+    assert_raise ExJsonSchema.Schema.UndefinedRemoteSchemaResolverError, fn -> resolve(schema) end
+    Application.put_env(:ex_json_schema, :remote_schema_resolver, resolver)
+  end
+end