Support injecting mock functionality into modules

Add mock registry for a single module.

spec/docs/mocks_spec.cr

@@ -205,6 +205,25 @@ Spectator.describe "Mocks Docs" do
       runnable = mock(Runnable2, command: "echo foo")
       expect(runnable.run_one).to eq("Running echo foo")
     end
+
+    context "Injecting Mocks" do
+      module MyFileUtils
+        def self.rm_rf(path)
+          true
+        end
+      end
+
+      inject_mock MyFileUtils do
+        stub def self.rm_rf(path)
+          "Simulating deletion of #{path}"
+          false
+        end
+      end
+
+      specify do
+        expect(MyFileUtils.rm_rf("/")).to be_false
+      end
+    end
   end
 
   context "Injecting Mocks" do

src/spectator/mocks/mock.cr

@@ -1,5 +1,6 @@
 require "./method_call"
 require "./mocked"
+require "./mock_registry"
 require "./reference_mock_registry"
 require "./stub"
 require "./stubbed_name"
@@ -157,7 +158,7 @@ module Spectator
           {% elsif base == :struct %}
             @@_spectator_mock_registry = ::Spectator::ValueMockRegistry(self).new
           {% else %}
-            {% raise "Unsupported base type #{base} for injecting mock" %}
+            @@_spectator_mock_registry = ::Spectator::MockRegistry.new
           {% end %}
 
           private class_getter _spectator_stubs : ::Array(::Spectator::Stub) = [] of ::Spectator::Stub

src/spectator/mocks/mock_registry.cr

@@ -0,0 +1,43 @@
+require "./mock_registry_entry"
+require "./stub"
+
+module Spectator
+  # Stores collections of stubs for mocked types.
+  #
+  # This type is intended for all mocked modules that have functionality "injected."
+  # That is, the type itself has mock functionality bolted on.
+  # Adding instance members should be avoided, for instance, it could mess up serialization.
+  class MockRegistry
+    @entry : MockRegistryEntry?
+
+    # Retrieves all stubs.
+    def [](_object = nil)
+      @entry.not_nil!
+    end
+
+    # Retrieves all stubs.
+    def []?(_object = nil)
+      @entry
+    end
+
+    # Retrieves all stubs.
+    #
+    # Yields to the block on the first retrieval.
+    # This allows a mock to populate the registry with initial stubs.
+    def fetch(object : Reference, & : -> Array(Stub))
+      entry = @entry
+      if entry.nil?
+        entry = MockRegistryEntry.new
+        entry.stubs = yield
+        @entry = entry
+      else
+        entry
+      end
+    end
+
+    # Clears all stubs defined for a mocked object.
+    def delete(object : Reference) : Nil
+      @entry = nil
+    end
+  end
+end