Add getter for wrapped instance

src/spectator/dsl/structure_dsl.cr

@@ -1002,6 +1002,9 @@ module Spectator::DSL
           @instance = {{wrapper_class_name.id}}.new(sample_values)
         end
 
+        # Retrieves the underlying, wrapped instance.
+        getter instance
+
         # Add the block's content if one was provided.
         {% if block.is_a?(Block) %}
           {{block.body}}

src/spectator/dummy_example.cr

@@ -14,6 +14,11 @@ module Spectator
       "DUMMY"
     end
 
+    # Dummy instance.
+    def instance
+      nil
+    end
+
     # Dummy run that does nothing.
     def run_instance
       raise "You shouldn't be running this."

src/spectator/example.cr

@@ -2,7 +2,7 @@ require "./example_component"
 
 module Spectator
   # Base class for all types of examples.
-  # Concrete types must implement the `#run_inner` and `#what` methods.
+  # Concrete types must implement the `#run_inner`, `#what`, and `#instance` methods.
   abstract class Example < ExampleComponent
     # Indicates whether the example has already been run.
     getter? finished = false
@@ -10,6 +10,9 @@ module Spectator
     # Group that the example belongs to.
     getter group : ExampleGroup
 
+    # Retrieves the internal wrapped instance.
+    abstract def instance
+
     # Runs the example code.
     # A result is returned, which represents the outcome of the test.
     # An example can be run only once.