Some initial double code

src/spectator/double.cr

@@ -0,0 +1,9 @@
+module Spectator
+  module Double
+    macro stub(definition)
+      def {{definition.name.id}}
+        {{definition.block.body}}
+      end
+    end
+  end
+end

src/spectator/dsl/structure_dsl.cr

@@ -1437,6 +1437,22 @@ module Spectator::DSL
       {% debug %}
     end
 
+    macro double(name, &block)
+      {% if block.is_a?(Nop) %}
+        # Create an instance of the double.
+        Double{{name.id}}.new
+      {% else %}
+        # Define a double.
+        struct Double{{name.id}} # TODO: Use fresh variable %double
+          include ::Spectator::Double
+
+          {{block.body}}
+        end
+        # TODO: Register double in current context.
+      {% end %}
+      {% debug %}
+    end
+
     # Creates an example, or a test case.
     # The *what* argument describes "what" is being tested or asserted.
     # The block contains the code to run the test.

src/spectator/includes.cr

@@ -31,6 +31,7 @@ require "./nested_example_group"
 require "./root_example_group"
 
 require "./mock"
+require "./double"
 
 require "./config"
 require "./config_builder"