Add temp_config helper

spec/habitat_spec.cr

@@ -47,6 +47,18 @@ describe Habitat do
     FakeServer.settings.nilable_with_default.should be_nil
   end
 
+  it "can set and reset config using a block" do
+    setup_server(port: 3000)
+
+    FakeServer.temp_config(port: 4000, this_can_be_nil: "string!") do
+      FakeServer.settings.port.should eq 4000
+      FakeServer.settings.this_can_be_nil.should eq "string!"
+    end
+
+    FakeServer.settings.port.should eq 3000
+    FakeServer.settings.this_can_be_nil.should be_nil
+  end
+
   it "can check for missing settings" do
     setup_server
 

src/habitat.cr

@@ -36,6 +36,7 @@ class Habitat
 
   macro create
     include Habitat::SettingHelpers
+    include Habitat::TempConfig
     Habitat.track(\{{ @type }})
 
     REQUIRED_SETTINGS = [] of TypeDeclaration
@@ -58,6 +59,19 @@ class Habitat
     {{ yield }}
   end
 
+  module TempConfig
+    macro temp_config(**settings_with_values)
+      {% for setting_name, setting_value in settings_with_values %}
+        original_{{ setting_name }} = {{ @type.name }}.settings.{{setting_name}}
+        {{ @type.name }}.settings.{{ setting_name }} = {{ setting_value }}
+      {% end %}
+      {{ yield }}
+      {% for setting_name, _unused in settings_with_values %}
+        {{ @type.name }}.settings.{{ setting_name }} = original_{{ setting_name }}
+      {% end %}
+    end
+  end
+
   module SettingHelpers
     macro setting(decl)
       {% if decl.type.is_a?(Union) && decl.type.types.map(&.id).includes?(Nil.id) %}