diff --git a/src/spectator/harness.cr b/src/spectator/harness.cr
index 88873e3..70ad610 100644
--- a/src/spectator/harness.cr
+++ b/src/spectator/harness.cr
@@ -27,8 +27,7 @@ module Spectator
     # The *example* argument will be the example to run.
     # The result returned from `Example#run` will be returned.
     def self.run(example : Example) : Result
-      @@current = harness = new(example)
-      harness.mocks.prepare(example.group.context)
+      @@current = new(example)
       example.run
     ensure
       @@current = nil
@@ -37,7 +36,7 @@ module Spectator
     # Retrieves the current running example.
     getter example : Example
 
-    getter mocks = Mocks::Registry.new
+    getter mocks : Mocks::Registry
 
     # Retrieves the group for the current running example.
     def group
@@ -60,6 +59,7 @@ module Spectator
     # The example the harness is for should be passed in.
     private def initialize(@example)
       @reporter = Expectations::ExpectationReporter.new
+      @mocks = Mocks::Registry.new(@example.group.context.stubs)
     end
   end
 end
diff --git a/src/spectator/mocks/registry.cr b/src/spectator/mocks/registry.cr
index d19119f..31c956b 100644
--- a/src/spectator/mocks/registry.cr
+++ b/src/spectator/mocks/registry.cr
@@ -10,8 +10,12 @@ module Spectator::Mocks
     @all_instances = {} of String => Entry
     @entries = {} of Key => Entry
 
-    def prepare(context : TestContext) : Nil
-      # TODO
+    def initialize(default_stubs)
+      @all_instances = default_stubs.map do |k, v|
+        entry = Entry.new
+        entry.stubs.concat(v)
+        {k, entry}
+      end.to_h
     end
 
     def reset : Nil
diff --git a/src/spectator/spec_builder.cr b/src/spectator/spec_builder.cr
index 07ddf8c..9e199c2 100644
--- a/src/spectator/spec_builder.cr
+++ b/src/spectator/spec_builder.cr
@@ -96,9 +96,8 @@ module Spectator
       @@stack.current.add_post_condition(block)
     end
 
-    def add_double(id : Symbol, double_type : Double.class) : Nil
-      double_factory = DoubleFactory.new(double_type)
-      current_group.add_double(id, double_factory)
+    def add_default_stub(*args) : Nil
+      @@stack.current.add_default_stub(*args)
     end
 
     # Builds the entire spec and returns it as a test suite.
diff --git a/src/spectator/spec_builder/example_group_builder.cr b/src/spectator/spec_builder/example_group_builder.cr
index f9ed5bf..90034b4 100644
--- a/src/spectator/spec_builder/example_group_builder.cr
+++ b/src/spectator/spec_builder/example_group_builder.cr
@@ -14,6 +14,7 @@ module Spectator::SpecBuilder
     @around_each_hooks = Deque(::SpectatorTest, Proc(Nil) ->).new
     @pre_conditions = Deque(TestMetaMethod).new
     @post_conditions = Deque(TestMetaMethod).new
+    @default_stubs = {} of String => Deque(Mocks::MethodStub)
 
     def add_child(child : Child)
       @children << child
@@ -47,6 +48,12 @@ module Spectator::SpecBuilder
       @post_conditions << hook
     end
 
+    def add_default_stub(type : T.class, stub : Mocks::MethodStub) forall T
+      key = type.name
+      @default_stubs[key] = Dequeue.new unless @default_stubs.has_key?(key)
+      @default_stubs[key] << stub
+    end
+
     private def build_hooks
       ExampleHooks.new(
         @before_all_hooks.to_a,
diff --git a/src/spectator/spec_builder/nested_example_group_builder.cr b/src/spectator/spec_builder/nested_example_group_builder.cr
index dc08cff..6d7bb77 100644
--- a/src/spectator/spec_builder/nested_example_group_builder.cr
+++ b/src/spectator/spec_builder/nested_example_group_builder.cr
@@ -7,7 +7,7 @@ module Spectator::SpecBuilder
     end
 
     def build(parent_group)
-      context = TestContext.new(parent_group.context, build_hooks, build_conditions, parent_group.context.values)
+      context = TestContext.new(parent_group.context, build_hooks, build_conditions, parent_group.context.values, @default_stubs)
       NestedExampleGroup.new(@description, @source, parent_group, context).tap do |group|
         group.children = children.map do |child|
           child.build(group).as(ExampleComponent)
diff --git a/src/spectator/spec_builder/root_example_group_builder.cr b/src/spectator/spec_builder/root_example_group_builder.cr
index 02f4914..3dbbcf7 100644
--- a/src/spectator/spec_builder/root_example_group_builder.cr
+++ b/src/spectator/spec_builder/root_example_group_builder.cr
@@ -4,7 +4,7 @@ require "./example_group_builder"
 module Spectator::SpecBuilder
   class RootExampleGroupBuilder < ExampleGroupBuilder
     def build
-      context = TestContext.new(nil, build_hooks, build_conditions, TestValues.empty)
+      context = TestContext.new(nil, build_hooks, build_conditions, TestValues.empty, {} of String => Deque(Mocks::MethodStub))
       RootExampleGroup.new(context).tap do |group|
         group.children = children.map do |child|
           child.build(group).as(ExampleComponent)
diff --git a/src/spectator/spec_builder/sample_example_group_builder.cr b/src/spectator/spec_builder/sample_example_group_builder.cr
index eacd596..955ac7a 100644
--- a/src/spectator/spec_builder/sample_example_group_builder.cr
+++ b/src/spectator/spec_builder/sample_example_group_builder.cr
@@ -9,7 +9,7 @@ module Spectator::SpecBuilder
     def build(parent_group)
       values = parent_group.context.values
       collection = @collection_builder.call(values)
-      context = TestContext.new(parent_group.context, build_hooks, build_conditions, values)
+      context = TestContext.new(parent_group.context, build_hooks, build_conditions, values, @default_stubs)
       NestedExampleGroup.new(@description, @source, parent_group, context).tap do |group|
         group.children = collection.map do |element|
           build_sub_group(group, element).as(ExampleComponent)
@@ -19,7 +19,7 @@ module Spectator::SpecBuilder
 
     private def build_sub_group(parent_group, element)
       values = parent_group.context.values.add(@id, @description.to_s, element)
-      context = TestContext.new(parent_group.context, ExampleHooks.empty, ExampleConditions.empty, values)
+      context = TestContext.new(parent_group.context, ExampleHooks.empty, ExampleConditions.empty, values, {} of String => Deque(Mocks::MethodStub))
       NestedExampleGroup.new("#{@label} = #{element.inspect}", @source, parent_group, context).tap do |group|
         group.children = children.map do |child|
           child.build(group).as(ExampleComponent)
diff --git a/src/spectator/test_context.cr b/src/spectator/test_context.cr
index 8d16fee..fd735e2 100644
--- a/src/spectator/test_context.cr
+++ b/src/spectator/test_context.cr
@@ -5,7 +5,13 @@ module Spectator
   class TestContext
     getter values
 
-    def initialize(@parent : TestContext?, @hooks : ExampleHooks, @conditions : ExampleConditions, @values : TestValues)
+    getter stubs : Hash(String, Deque(Mocks::MethodStub))
+
+    def initialize(@parent : TestContext?,
+      @hooks : ExampleHooks,
+      @conditions : ExampleConditions,
+      @values : TestValues,
+      @stubs : Hash(String, Deque(Mocks::MethodStub)))
       @before_all_hooks_run = false
       @after_all_hooks_run = false
     end