looks like its working

lib/shoulda/matchers/active_model/ensure_inclusion_of_matcher.rb

@@ -5,6 +5,7 @@ module Shoulda # :nodoc:
       # Ensure that the attribute's value is in the range specified
       #
       # Options:
+      # * <tt>in_array</tt> - the range of allowed values for this attribute
       # * <tt>in_range</tt> - the range of allowed values for this attribute
       # * <tt>with_low_message</tt> - value the test expects to find in
       #   <tt>errors.on(:attribute)</tt>. Regexp or string. Defaults to the
@@ -21,7 +22,12 @@ module Shoulda # :nodoc:
       end
 
       class EnsureInclusionOfMatcher < ValidationMatcher # :nodoc:
-
+        
+        def in_array(array)
+          @array = array
+          self
+        end
+        
         def in_range(range)
           @range = range
           @minimum = range.first
@@ -47,24 +53,43 @@ module Shoulda # :nodoc:
           self
         end
 
+        
         def description
-          "ensure inclusion of #{@attribute} in #{@range.inspect}"
+          "ensure inclusion of #{@attribute} in #{inspect_message}"
         end
 
         def matches?(subject)
           super(subject)
 
-          @low_message  ||= :inclusion
-          @high_message ||= :inclusion
+          if @range
+            @low_message  ||= :inclusion
+            @high_message ||= :inclusion
 
-          disallows_lower_value &&
-            allows_minimum_value &&
-            disallows_higher_value &&
-            allows_maximum_value
+            disallows_lower_value &&
+              allows_minimum_value &&
+              disallows_higher_value &&
+              allows_maximum_value
+          elsif @array
+            unless allows_all_values_in_array
+              @failure_message = "#{@array} doesn't include #{@attribute}"
+              return false
+            end
+            true
+          end
         end
 
         private
 
+        def inspect_message
+          @range.nil? ? @array.inspect : @range.inspect 
+        end
+
+        def allows_all_values_in_array
+          @array.any? do |value|
+            allows_value_of(@attribute, :inclusion)
+          end
+        end
+              
         def disallows_lower_value
           @minimum == 0 || disallows_value_of(@minimum - 1, @low_message)
         end

lib/shoulda/matchers/active_model/validation_matcher.rb

@@ -18,7 +18,7 @@ module Shoulda # :nodoc:
         end
 
         private
-
+        
         def allows_value_of(value, message = nil)
           allow = AllowValueMatcher.
             new(value).

spec/shoulda/active_model/ensure_inclusion_of_matcher_spec.rb

@@ -68,4 +68,44 @@ describe Shoulda::Matchers::ActiveModel::EnsureInclusionOfMatcher do
 
   end
 
+  context "an attribute which must be included in a array" do
+    before do
+      @model = define_model(:example_foo, :attr => :boolean) do
+        validates_inclusion_of :attr, :in => [true,false]
+      end.new(:attr=>true)
+    end
+
+    it "should accept ensuring the correct array" do
+      @model.should ensure_inclusion_of(:attr).in_array [true,false]
+    end
+    it "should have the array in the description" do
+      ensure_inclusion_of(:attr).in_array([true,false]).description.should  ==  "ensure inclusion of attr in [true, false]"
+    end
+  end
+  
+  context "an attribute not included in the array" do
+    before do
+      @model = define_model(:example_foo, :attr => :boolean) do
+        validate :custom_validation
+        def custom_validation
+          unless [true,false].include? attr 
+            errors.add(:attr, 'not boolean')
+          end
+        end
+      end.new
+    end
+
+    it "should have an error on attr" do
+      @model.should ensure_inclusion_of(:attr).in_array([true,false]).with_message(/boolean/)
+    end
+    context "should not accept other value then specified" do
+      before do
+        @model.attr = "foo"
+      end
+      it  "should not be valid" do
+        @model.should ensure_inclusion_of(:attr).in_array([true,false]).with_message(/inclusion/)
+      end
+    end
+  end
+  
 end