Expect messages on double, but don't stub them

src/spectator/expectations/expectation_partial.cr

@@ -25,6 +25,7 @@ module Spectator::Expectations
     end
 
     def to(stub : Mocks::MethodStub) : Nil
+      Harness.current.mocks.expect(@actual.value, stub.name)
       value = TestValue.new(stub.name, stub.to_s)
       matcher = if (arguments = stub.arguments?)
                   Matchers::ReceiveArgumentsMatcher.new(value, arguments)

src/spectator/mocks/double.cr

@@ -62,7 +62,10 @@ module Spectator::Mocks
         {% if body && !body.is_a?(Nop) %}
           {{body.body}}
         {% else %}
-          raise ::Spectator::Mocks::UnexpectedMessageError.new("#{self} received unexpected message {{name}}")
+          unless ::Spectator::Harness.current.mocks.expected?(self, {{name.symbolize}})
+            raise ::Spectator::Mocks::UnexpectedMessageError.new("#{self} received unexpected message {{name}}")
+          end
+
           # This code shouldn't be reached, but makes the compiler happy to have a matching return type.
           {% if definition.is_a?(TypeDeclaration) %}
             %x = uninitialized {{definition.type}}
@@ -75,6 +78,7 @@ module Spectator::Mocks
 
     macro method_missing(call)
       return self if @null
+      return self if ::Spectator::Harness.current.mocks.expected?(self, {{call.name.symbolize}})
 
       raise ::Spectator::Mocks::UnexpectedMessageError.new("#{self} received unexpected message {{call.name}}")
     end

src/spectator/mocks/registry.cr

@@ -5,6 +5,7 @@ module Spectator::Mocks
     private struct Entry
       getter stubs = Deque(MethodStub).new
       getter calls = Deque(MethodCall).new
+      getter expected = Set(Symbol).new
     end
 
     @all_instances = {} of String => Entry
@@ -64,6 +65,14 @@ module Spectator::Mocks
       fetch_type(type).calls.select { |call| call.name == method_name }
     end
 
+    def expected?(object, method_name : Symbol) : Bool
+      fetch_instance(object).expected.includes?(method_name)
+    end
+
+    def expect(object, method_name : Symbol) : Nil
+      fetch_instance(object).expected.add(method_name)
+    end
+
     private def fetch_instance(object)
       key = unique_key(object)
       if @entries.has_key?(key)